US20100081154A1 - IDENTIFICATION AND USE OF BACTERIAL [2Fe-2S] DIHYDROXY-ACID DEHYDRATASES - Google Patents

IDENTIFICATION AND USE OF BACTERIAL [2Fe-2S] DIHYDROXY-ACID DEHYDRATASES Download PDF

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US20100081154A1
US20100081154A1 US12/569,636 US56963609A US2010081154A1 US 20100081154 A1 US20100081154 A1 US 20100081154A1 US 56963609 A US56963609 A US 56963609A US 2010081154 A1 US2010081154 A1 US 2010081154A1
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dhad
sequences
sequence
bacterial
cell
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Dennis Flint
Steven Cary Rothman
Wonchul Suh
Jean-Francois Tomb
Rick W. Ye
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Butamax Advanced Biofuels LLC
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Publication of US20100081154A1 publication Critical patent/US20100081154A1/en
Assigned to BUTAMAX ADVANCED BIOFUELS LLC reassignment BUTAMAX ADVANCED BIOFUELS LLC ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: E. I. DU PONT DE NEMOURS AND COMPANY
Priority to US13/838,570 priority patent/US20140051137A1/en
Priority to US13/838,508 priority patent/US8951937B2/en
Priority to US15/016,759 priority patent/US20160222370A1/en
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    • G—PHYSICS
    • G16—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR SPECIFIC APPLICATION FIELDS
    • G16B—BIOINFORMATICS, i.e. INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR GENETIC OR PROTEIN-RELATED DATA PROCESSING IN COMPUTATIONAL MOLECULAR BIOLOGY
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    • C12N15/00—Mutation or genetic engineering; DNA or RNA concerning genetic engineering, vectors, e.g. plasmids, or their isolation, preparation or purification; Use of hosts therefor
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    • C12N15/00—Mutation or genetic engineering; DNA or RNA concerning genetic engineering, vectors, e.g. plasmids, or their isolation, preparation or purification; Use of hosts therefor
    • C12N15/09—Recombinant DNA-technology
    • C12N15/63—Introduction of foreign genetic material using vectors; Vectors; Use of hosts therefor; Regulation of expression
    • C12N15/74—Vectors or expression systems specially adapted for prokaryotic hosts other than E. coli, e.g. Lactobacillus, Micromonospora
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    • C12N15/00—Mutation or genetic engineering; DNA or RNA concerning genetic engineering, vectors, e.g. plasmids, or their isolation, preparation or purification; Use of hosts therefor
    • C12N15/09—Recombinant DNA-technology
    • C12N15/63—Introduction of foreign genetic material using vectors; Vectors; Use of hosts therefor; Regulation of expression
    • C12N15/79—Vectors or expression systems specially adapted for eukaryotic hosts
    • C12N15/80—Vectors or expression systems specially adapted for eukaryotic hosts for fungi
    • C12N15/81—Vectors or expression systems specially adapted for eukaryotic hosts for fungi for yeasts
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    • C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
    • C12N9/88—Lyases (4.)
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    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
    • C12P13/00—Preparation of nitrogen-containing organic compounds
    • C12P13/04—Alpha- or beta- amino acids
    • C12P13/06—Alanine; Leucine; Isoleucine; Serine; Homoserine
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
    • C12P13/00—Preparation of nitrogen-containing organic compounds
    • C12P13/04—Alpha- or beta- amino acids
    • C12P13/08—Lysine; Diaminopimelic acid; Threonine; Valine
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
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    • C12P7/00—Preparation of oxygen-containing organic compounds
    • C12P7/02—Preparation of oxygen-containing organic compounds containing a hydroxy group
    • C12P7/04—Preparation of oxygen-containing organic compounds containing a hydroxy group acyclic
    • C12P7/16—Butanols
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
    • C12P7/00—Preparation of oxygen-containing organic compounds
    • C12P7/40—Preparation of oxygen-containing organic compounds containing a carboxyl group including Peroxycarboxylic acids
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Y—ENZYMES
    • C12Y402/00—Carbon-oxygen lyases (4.2)
    • C12Y402/01—Hydro-lyases (4.2.1)
    • C12Y402/01009—Dihydroxy-acid dehydratase (4.2.1.9), i.e. acetohydroxyacid dehydratase
    • G—PHYSICS
    • G16—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR SPECIFIC APPLICATION FIELDS
    • G16B—BIOINFORMATICS, i.e. INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR GENETIC OR PROTEIN-RELATED DATA PROCESSING IN COMPUTATIONAL MOLECULAR BIOLOGY
    • G16B30/00—ICT specially adapted for sequence analysis involving nucleotides or amino acids
    • G16B30/10—Sequence alignment; Homology search
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E50/00—Technologies for the production of fuel of non-fossil origin
    • Y02E50/10—Biofuels, e.g. bio-diesel

Definitions

  • the invention relates to the field of industrial microbiology and the expression of dihydroxy-acid dehydratase activity. More specifically, bacterial dihydroxy-acid dehydratases with a [2Fe-2S] cluster are identified and expressed as heterologous proteins in bacterial and yeast hosts.
  • DHAD Dihydroxy-acid dehydratase
  • acetohydroxy acid dehydratase catalyzes the conversion of 2,3-dihydroxyisovalerate to ⁇ -ketoisovalerate and of 2,3-dihydroxymethylvalerate to ⁇ -ketomethylvalerate.
  • the DHAD enzyme classified as E.C. 4.2.1.9, is part of naturally occurring biosynthetic pathways producing valine, isoleucine, leucine and pantothenic acid (vitamin B5). Increased expression of DHAD activity is desired for enhanced microbial production of branched chain amino acids or of pantothenic acid.
  • DHAD catalyzed conversion of 2,3-dihydroxyisovalerate to ⁇ -ketoisovalerate is also a common step in the multiple isobutanol biosynthetic pathways that are disclosed in commonly owned and co-pending US Patent Application Publication US 20070092957 A1.
  • Disclosed therein is engineering of recombinant microorganisms for production of isobutanol. Isobutanol is useful as a fuel additive, whose availability may reduce the demand for petrochemical fuels.
  • a heterologous enzyme that provides this enzymatic activity in the production host of interest.
  • Obtaining high functional expression of dihydroxy-acid dehydratases in a heterologous host is complicated by the enzyme's requirement for an Fe—S cluster, which involves availability and proper loading of the cluster into the DHAD apo-protein.
  • Fe—S cluster requiring DHAD enzymes are known in the art and are found either in the [4Fe-4S] or [2Fe-2S] form.
  • Some bacterial enzymes are known, the best characterized of which is from E. coli (Flint, D H, et al. (1993) J. Biol. Chem. 268:14732-14742). However these bacterial enzymes are all in the [4Fe-4S] form.
  • the only [2Fe-2S] form reported to date is a spinach enzyme (Flint and Emptage (1988) J. Biol. Chem. 263:3558-3564).
  • step (a) analyzing the first subset of sequences that correspond to one or more DHAD related proteins of step (a) for the presence of three conserved cysteines that correspond to positions 56, 129, and 201 in the Streptococcus mutans dihydroxy-acid dehydratase amino acid sequence (SEQ ID NO: 168) whereby a second subset of sequences encoding [2Fe-2S] DHAD enzymes are identified; and
  • step (b) analyzing said second subset of sequences of step (b) for the presence of signature conserved amino acids at positions corresponding to positions in the Streptococcus mutans DHAD amino acid sequence (SEQ ID NO: 168) that are aspartic acid at position 88, arginine or asparagine at position 142, asparagine at position 208, and leucine at position 454 whereby a third subset of sequences encoding [2Fe-2S] DHAD enzymes are further identified.
  • the above method further comprises:
  • the method above further comprises:
  • the method above further comprises selecting one or more sequences corresponding to bacterial [2Fe-2S] DHAD enzyme sequences identified in any one or all of steps a), b), and c). Said selected sequences may be expressed in a cell; and the DHAD activity in the cell may be confirmed. Said selected sequences may be further purified such that a purified protein is obtained and the [2Fe-2S] DHAD enzyme activity of said purified protein may be confirmed by UV-vis and EPR spectroscopy.
  • Another aspect of the invention is directed to a microbial host cell comprising at least one heterologous [2Fe-2S] DHAD enzyme identifiable by the methods described herein.
  • Said cell maybe a bacterial cell or a yeast cell.
  • the cell may also be a recombinant cell that produces isobutanol.
  • Another aspect of the invention is a method for the production of isobutanol comprising:
  • step (b) growing the host cell of step (a) under conditions wherein isobutanol is produced.
  • Another aspect of the invention is a method for the conversion of 2,3-dihydroxyisovalerate to ⁇ -ketoisovalerate comprising:
  • FIG. 1 shows the conserved cysteine regions, with C for cysteine in bold, in representative bacterial [2Fe-2S] DHADs and a [4Fe-4S] DHAD. Single letter amino acid abbreviations are used.
  • FIG. 2 shows a phylogenetic tree of DHAD related proteins. Branches for [4Fe-4S] and [2Fe-2S] DHADs as well as EDDs, aldonic acid dehydratases and an undefined group (Und) are marked. Select individual DHADs are labeled.
  • FIG. 3 shows biosynthetic pathways for isobutanol production.
  • FIG. 4 shows graphs of stability of activity in air of A) S. mutans DHAD, and B) E. coli DHAD.
  • FIG. 5 shows a plot of the UV-visible spectrum of S. mutans DHAD.
  • FIG. 6 shows a plot of the electron paramagnetic resonance (EPR) spectrum of S. mutans DHAD at different temperatures between 20° K. and 90° K.
  • EPR electron paramagnetic resonance
  • FIG. 7 shows HPLC analysis of an extract of yeast cells that express acetolactate synthase, KARI, and S. mutans DHAD genes, with an isobutanol peak at 47.533 minutes.
  • FIG. 8 shows a graph of stability of L. lactis DHAD in air.
  • FIG. 9 shows a plot of the UV-visible spectrum of the purified L. lactis DHAD.
  • Table 1 is a table of the Profile HMM for dihydroxy-acid dehydratases based on enzymes with assayed function prepared as described in Example 1. Table 1 is submitted herewith electronically and is incorporated herein by reference.
  • ORS278 55 56 Bradyrhizobium japonicum USDA 110 57 58 Fulvimarina pelagi HTCC2506 59 60 Aurantimonas sp. SI85-9A1 61 62 Hoeflea phototrophica DFL-43 63 64 Mesorhizobium loti MAFF303099 65 66 Mesorhizobium sp. BNC1 67 68 Parvibaculum lavamentivorans DS-1 69 70 Loktanella vestfoldensis SKA53 71 72 Roseobacter sp.
  • NAP1 107
  • Comamonas testosterone KF-1 109
  • Sphingomonas wittichii RW1 111
  • Burkholderia xenovorans LB400 113
  • Burkholderia phytofirmans PsJN
  • PsJN 115
  • Bordetella petrii DSM 12804 117
  • Bordetella bronchiseptica RB50 120 Bradyrhizobium sp.
  • ORS278 121 122 Bradyrhizobium sp.
  • MED134 203 Kordia algicida OT-1 205 206 Flavobacteriales bacterium ALC-1 207 208 Psychroflexus torquis ATCC 700755 209 210 Flavobacteriales bacterium HTCC2170 211 212 unidentified eubacterium SCB49 213 214 Gramella forsetii KT0803 215 216 Robiginitalea biformata HTCC2501 217 218 Tenacibaculum sp. MED152 219 220 Polaribacter irgensii 23-P 221 222 Pedobacter sp.
  • EbN1 331 332 Burkholderia phymatum STM815 333 334 Burkholderia xenovorans LB400 335 336 Burkholderia multivorans ATCC 17616 337 338 Burkholderia cenocepacia PC184 339 340 Burkholderia mallei GB8 horse 4 341 342 Ralstonia eutropha JMP134 343 344 Ralstonia metallidurans CH34 345 346 Ralstonia solanacearum UW551 347 348 Ralstonia pickettii 12J 349 350 Limnobacter sp.
  • MED105 351 352 Herminiimonas arsenicoxydans 353 354 Bordetella parapertussis 355 356 Bordetella petrii DSM 12804 357 358 Polaromonas sp.
  • JS666 359 360 Polaromonas naphthalenivorans CJ2 361 362 Rhodoferax ferrireducens T118 363 364 Verminephrobacter eiseniae EF01-2 365 366 Acidovorax sp.
  • BTAi1 445 446 Delftia acidovorans SPH-1 447 448 Microcystis aeruginosa NIES-843 449 450 uncultured marine microorganism 451 452 HF4000_APKG8C21 Burkholderia ubonensis Bu 453 454 Gemmata obscuriglobus UQM 2246 455 456 Mycobacterium abscessus 457 458 Synechococcus sp.
  • PCC 7002 459 460 Burkholderia graminis C4D1M 461 462 Methylobacterium radiotolerans JCM 2831 463 464 Leptothrix cholodnii SP-6 465 466 Verrucomicrobium spinosum DSM 4136 467 468 Cyanothece sp.
  • SEQ ID NOs: 395-409, 412-421, 424, and 431-436 are primers for PCR, cloning or sequencing analysis used a described in the Examples herein.
  • SEQ ID NO: 410 is the nucleotide sequence of the pDM1 vector.
  • SEQ ID NO: 411 is the nucleotide sequence of the pLH532 vector.
  • SEQ ID NO: 425 is the S. cerevisiae FBA promoter.
  • SEQ ID NO: 430 is the nucleotide sequence of the pRS423 FBA ilvD(Strep) vector.
  • SEQ ID NO: 437 is the nucleotide sequence of the pNY13 vector
  • SEQ ID NO: 438 is the alsS coding region from B. subtilis .
  • SEQ ID NO: 439 is the S. cerevisiae GPD promoter.
  • SEQ ID NO: 440 is the S. cerevisiae CYC1 terminator.
  • SEQ ID NO: 442 is the S. cerevisiae ILV5 gene.
  • the present invention relates to recombinant yeast or bacterial cells engineered to provide heterologous expression of dihydroxy-acid dehydratase (DHAD) having a [2Fe-2S] cluster.
  • DHAD dihydroxy-acid dehydratase
  • the expressed DHAD functions as a component of a biosynthetic pathway for production of a compound such as valine, isoleucine, leucine, pantothenic acid, or isobutanol.
  • These amino acids and pantothenic acid may be used as nutritional supplements, and isobutanol may be used as a fuel additive to reduce demand for petrochemicals.
  • the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” “contains” or “containing,” or any other variation thereof, are intended to cover a non-exclusive inclusion.
  • a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus.
  • “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).
  • invention or “present invention” as used herein is a non-limiting term and is not intended to refer to any single embodiment of the particular invention but encompasses all possible embodiments as described in the specification and the claims.
  • the term “about” modifying the quantity of an ingredient or reactant of the invention employed refers to variation in the numerical quantity that can occur, for example, through typical measuring and liquid handling procedures used for making concentrates or use solutions in the real world; through inadvertent error in these procedures; through differences in the manufacture, source, or purity of the ingredients employed to make the compositions or carry out the methods; and the like.
  • the term “about” also encompasses amounts that differ due to different equilibrium conditions for a composition resulting from a particular initial mixture. Whether or not modified by the term “about”, the claims include equivalents to the quantities.
  • the term “about” means within 10% of the reported numerical value, preferably within 5% of the reported numerical value
  • [2Fe-2S] DHAD refers to DHAD enzymes having a bound [2Fe-2S] cluster.
  • [4Fe-4S] DHAD refers to DHAD enzymes having a bound [4Fe-4S] cluster.
  • DHAD dihydroxy-acid dehydratase
  • isobutanol biosynthetic pathway refers to an enzyme pathway to produce isobutanol from pyruvate.
  • a facultative anaerobe refers to a microorganism that can grow in both aerobic and anaerobic environments.
  • carbon substrate or “fermentable carbon substrate” refers to a carbon source capable of being metabolized by host organisms of the present invention and particularly carbon sources selected from the group consisting of monosaccharides, oligosaccharides, polysaccharides, and one-carbon substrates or mixtures thereof. Carbon substrates may include C6 and C5 sugars and mixtures thereof.
  • gene refers to a nucleic acid fragment that is capable of being expressed as a specific protein, optionally including regulatory sequences preceding (5′ non-coding sequences) and following (3′ non-coding sequences) the coding sequence.
  • “Native gene” refers to a gene as found in nature with its own regulatory sequences.
  • “Chimeric gene” refers to any gene that is not a native gene, comprising regulatory and coding sequences that are not found together in nature. Accordingly, a chimeric gene may comprise regulatory sequences and coding sequences that are derived from different sources, or regulatory sequences and coding sequences derived from the same source, but arranged in a manner different than that found in nature.
  • Endogenous gene refers to a native gene in its natural location in the genome of an organism.
  • a “foreign gene” or “heterologous gene” refers to a gene not normally found in the host organism, but that is introduced into the host organism by gene transfer.
  • Foreign genes can comprise native genes inserted into a non-native organism, or chimeric genes.
  • a “transgene” is a gene that has been introduced into the genome by a transformation procedure.
  • coding region refers to a DNA sequence that codes for a specific amino acid sequence.
  • Suitable regulatory sequences refer to nucleotide sequences located upstream (5′ non-coding sequences), within, or downstream (3′ non-coding sequences) of a coding sequence, and which influence the transcription, RNA processing or stability, or translation of the associated coding sequence. Regulatory sequences may include promoters, translation leader sequences, introns, polyadenylation recognition sequences, RNA processing site, effector binding site and stem-loop structure.
  • promoter refers to a DNA sequence capable of controlling the expression of a coding sequence or functional RNA.
  • a coding sequence is located 3′ to a promoter sequence. Promoters may be derived in their entirety from a native gene, or be composed of different elements derived from different promoters found in nature, or even comprise synthetic DNA segments. It is understood by those skilled in the art that different promoters may direct the expression of a gene in different tissues or cell types, or at different stages of development, or in response to different environmental or physiological conditions. Promoters which cause a gene to be expressed in most cell types at most times are commonly referred to as “constitutive promoters”. It is further recognized that since in most cases the exact boundaries of regulatory sequences have not been completely defined, DNA fragments of different lengths may have identical promoter activity.
  • operably linked refers to the association of nucleic acid sequences on a single nucleic acid fragment so that the function of one is affected by the other.
  • a promoter is operably linked with a coding sequence when it is capable of effecting the expression of that coding sequence (i.e., that the coding sequence is under the transcriptional control of the promoter).
  • Coding sequences can be operably linked to regulatory sequences in sense or antisense orientation.
  • expression refers to the transcription and stable accumulation of sense (mRNA) or antisense RNA derived from the nucleic acid fragment of the invention. Expression may also refer to translation of mRNA into a polypeptide.
  • transformation refers to the transfer of a nucleic acid fragment into a host organism, resulting in genetically stable inheritance.
  • Host organisms containing the transformed nucleic acid fragments are referred to as “transgenic” or “recombinant” or “transformed” organisms.
  • Plasmid and “vector” as used herein, refer to an extra chromosomal element often carrying genes which are not part of the central metabolism of the cell, and usually in the form of circular double-stranded DNA molecules.
  • Such elements may be autonomously replicating sequences, genome integrating sequences, phage or nucleotide sequences, linear or circular, of a single- or double-stranded DNA or RNA, derived from any source, in which a number of nucleotide sequences have been joined or recombined into a unique construction which is capable of introducing a promoter fragment and DNA sequence for a selected gene product along with appropriate 3′ untranslated sequence into a cell.
  • cognate degeneracy refers to the nature in the genetic code permitting variation of the nucleotide sequence without effecting the amino acid sequence of an encoded polypeptide.
  • the skilled artisan is well aware of the “codon-bias” exhibited by a specific host cell in usage of nucleotide codons to specify a given amino acid. Therefore, when synthesizing a gene for improved expression in a host cell, it is desirable to design the gene such that its frequency of codon usage approaches the frequency of preferred codon usage of the host cell.
  • codon-optimized refers to genes or coding regions of nucleic acid molecules for transformation of various hosts, refers to the alteration of codons in the gene or coding regions of the nucleic acid molecules to reflect the typical codon usage of the host organism without altering the polypeptide encoded by the DNA.
  • an “isolated nucleic acid fragment” or “isolated nucleic acid molecule” will be used interchangeably and will mean a polymer of RNA or DNA that is single- or double-stranded, optionally containing synthetic, non-natural or altered nucleotide bases.
  • An isolated nucleic acid fragment in the form of a polymer of DNA may be comprised of one or more segments of cDNA, genomic DNA or synthetic DNA.
  • a nucleic acid fragment is “hybridizable” to another nucleic acid fragment, such as a cDNA, genomic DNA, or RNA molecule, when a single-stranded form of the nucleic acid fragment can anneal to the other nucleic acid fragment under the appropriate conditions of temperature and solution ionic strength.
  • Hybridization and washing conditions are well known and exemplified in Sambrook, J., Fritsch, E. F. and Maniatis, T. Molecular Cloning: A Laboratory Manual, 2 nd ed., Cold Spring Harbor Laboratory: Cold Spring Harbor, N.Y. (1989), particularly Chapter 11 and Table 11.1 therein (entirely incorporated herein by reference).
  • Stringency conditions can be adjusted to screen for moderately similar fragments (such as homologous sequences from distantly related organisms), to highly similar fragments (such as genes that duplicate functional enzymes from closely related organisms).
  • Post-hybridization washes determine stringency conditions.
  • One set of preferred conditions uses a series of washes starting with 6 ⁇ SSC, 0.5% SDS at room temperature for 15 min, then repeated with 2 ⁇ SSC, 0.5% SDS at 45° C. for 30 min, and then repeated twice with 0.2 ⁇ SSC, 0.5% SDS at 50° C. for 30 min.
  • a more preferred set of stringent conditions uses higher temperatures in which the washes are identical to those above except for the temperature of the final two 30 min washes in 0.2 ⁇ SSC, 0.5% SDS was increased to 60° C.
  • Another preferred set of highly stringent conditions uses two final washes in 0.1 ⁇ SSC, 0.1% SDS at 65° C.
  • An additional set of stringent conditions include hybridization at 0.1 ⁇ SSC, 0.1% SDS, 65° C. and washes with 2 ⁇ SSC, 0.1% SDS followed by 0.1 ⁇ SSC, 0.1% SDS, for example.
  • Hybridization requires that the two nucleic acids contain complementary sequences, although depending on the stringency of the hybridization, mismatches between bases are possible.
  • the appropriate stringency for hybridizing nucleic acids depends on the length of the nucleic acids and the degree of complementation, variables well known in the art. The greater the degree of similarity or homology between two nucleotide sequences, the greater the value of Tm for hybrids of nucleic acids having those sequences.
  • the relative stability (corresponding to higher Tm) of nucleic acid hybridizations decreases in the following order: RNA:RNA, DNA:RNA, DNA:DNA.
  • the length for a hybridizable nucleic acid is at least about 10 nucleotides.
  • a minimum length for a hybridizable nucleic acid is at least about 15 nucleotides; more preferably at least about 20 nucleotides; and most preferably the length is at least about 30 nucleotides.
  • the temperature and wash solution salt concentration may be adjusted as necessary according to factors such as length of the probe.
  • a “substantial portion” of an amino acid or nucleotide sequence is that portion comprising enough of the amino acid sequence of a polypeptide or the nucleotide sequence of a gene to putatively identify that polypeptide or gene, either by manual evaluation of the sequence by one skilled in the art, or by computer-automated sequence comparison and identification using algorithms such as BLAST (Altschul, S. F., et al., J. Mol. Biol., 215:403-410 (1993)). In general, a sequence of ten or more contiguous amino acids or thirty or more nucleotides is necessary in order to putatively identify a polypeptide or nucleic acid sequence as homologous to a known protein or gene.
  • gene specific oligonucleotide probes comprising 20-30 contiguous nucleotides may be used in sequence-dependent methods of gene identification (e.g., Southern hybridization) and isolation (e.g., in situ hybridization of bacterial colonies or bacteriophage plaques).
  • short oligonucleotides of 12-15 bases may be used as amplification primers in PCR in order to obtain a particular nucleic acid fragment comprising the primers.
  • a “substantial portion” of a nucleotide sequence comprises enough of the sequence to specifically identify and/or isolate a nucleic acid fragment comprising the sequence.
  • adenosine is complementary to thymine and cytosine is complementary to guanine.
  • identity is a relationship between two or more polypeptide sequences or two or more polynucleotide sequences, as determined by comparing the sequences.
  • identity or “sequence identity” also means the degree of sequence relatedness between polypeptide or polynucleotide sequences, as the case may be, as determined by the match between strings of such sequences. “Identity” and “similarity” can be readily calculated by known methods, including but not limited to those described in:
  • Preferred methods to determine identity are designed to give the best match between the sequences tested. Methods to determine identity and similarity are codified in publicly available computer programs. Sequence alignments and percent identity calculations may be performed using the MegAlignTM program of the LASERGENE bioinformatics computing suite (DNASTAR Inc., Madison, Wis.). Multiple alignment of the sequences is performed using the “Clustal method of alignment” which encompasses several varieties of the algorithm including the “Clustal V method of alignment” corresponding to the alignment method labeled Clustal V (described by Higgins and Sharp, CABIOS. 5:151-153 (1989); Higgins, D. G. et al., Comput. Appl.
  • Clustal W method of alignment is available and corresponds to the alignment method labeled Clustal W (described by Higgins and Sharp, CABIOS. 5:151-153 (1989); Higgins, D. G. et al., Comput. Appl. Biosci. 8:189-191 (1992) Thompson, J. D., Higgins, D. G., and Gibson T. J. (1994) Nuc. Acid Res.
  • percent identities include, but are not limited to: 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, or any integer percentage from 55% to 100% may be useful in describing the present invention, such as 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%.
  • Suitable nucleic acid fragments not only have the above homologies but typically encode a polypeptide having at least 50 amino acids, preferably at least 100 amino acids, more preferably at least 150 amino acids, still more preferably at least 200 amino acids, and most preferably at least 250 amino acids.
  • sequence analysis software refers to any computer algorithm or software program that is useful for the analysis of nucleotide or amino acid sequences. “Sequence analysis software” may be commercially available or independently developed. Typical sequence analysis software will include, but is not limited to: 1.) the GCG suite of programs (Wisconsin Package Version 9.0, Genetics Computer Group (GCG), Madison, Wis.); 2.) BLASTP, BLASTN, BLASTX (Altschul et al., J. Mol. Biol., 215:403-410 (1990)); 3.) DNASTAR (DNASTAR, Inc.
  • DHAD proteins are known to contain a bound iron-sulfur (Fe—S) cluster that is required for enzyme activity.
  • Fe—S iron-sulfur
  • the only DHAD with a [2Fe-2S] cluster reported to date is a spinach enzyme (Flint and Emptage (1988) J. Biol. Chem. 263:3558-3564).
  • Some bacterial enzymes are also known, the best characterized of which is from E. coli (Flint, D H, et al. (1993) J. Biol. Chem. 268:14732-14742), which has a [4Fe-4S] cluster.
  • Applicants have now determined that there is a class of bacterial DHADs that contain a [2Fe-2S] cluster ([2Fe-2S] DHADs).
  • [2Fe-2S] DHADs may be distinguished from a group of [4Fe-45] DHADs by the presence of three conserved cysteine residues in the protein.
  • the three conserved cysteines are similar to three essential cysteines reported in the Azospirillum brasiliense arabonate (an aldonic acid) dehydratase (Watanabe, S et al. J. Biol. Chem . (2006) 281:33521-33536) that was reported to contain a [4Fe-4S] cluster.
  • cysteines located at amino acid positions 56, 124, and 197 were determined to be essential for enzyme activity and likely involved in coordination with the Fe—S cluster.
  • three conserved cysteines, which are in corresponding positions to the three essential cysteines of the Azospirillum brasiliense arabonate dehydratase are characteristic of DHADs containing a [2Fe-2S] cluster.
  • the E. coli DHAD, that contains a [4Fe-4S] cluster has two of the conserved cysteines, but not the third conserved cysteine. Shown in FIG.
  • Example 1 is a comparison of the sequence regions of the conserved cysteines for the E. coli [ 4Fe-4S] cluster-containing DHADs and for representatives of a phylogenetic group of [2Fe-2S] cluster DHADs that was identified herein in Example 1 and is described below.
  • bacterial [2Fe-2S] DHADs which may be identified by this method, may be used for heterologous expression in bacteria.
  • HMM Profile Hidden Markov Model
  • PCC6803 (DNA SEQ ID:297; Protein SEQ ID NO:298), Streptococcus mutans (DNA SEQ ID NO:167; Protein SEQ ID NO:168), Streptococcus thermophilus (DNA SEQ ID NO:163; SEQ ID No:164), Ralstonia metallidurans (DNA SEQ ID NO:345; Protein SEQ ID NO:346), Ralstonia eutropha (DNA SEQ ID NO:343; Protein SEQ ID NO:344), and Lactococcus lactis (DNA SEQ ID NO:231; Protein SEQ ID NO:232).
  • DHAD from Flavobacterium johnsoniae (DNA SEQ ID NO:229; Protein SEQ ID NO:230) was found to have dihydroxy-acid dehydratase activity when expressed in E. coli and was used in making the Profile.
  • This Profile HMM for DHADs may be used to identify DHAD related proteins. Any protein that matches the Profile HMM with an E value of ⁇ 10 ⁇ 5 is a DHAD related protein, which includes [4Fe-4S] DHADs, [2Fe-2S] DHADs, aldonic acid dehydratases, and phosphogluconate dehydratases. A phylogenetic tree of sequences matching this Profile HMM is shown in FIG. 2 .
  • Sequences matching the Profile HMM given herein are then analyzed for the presence of the three conserved cysteines described above.
  • the three conserved cysteines are located at amino acid positions 56, 129, and 201 in the Streptococcus mutans DHAD (SEQ ID NO: 168), and at amino acid positions 61, 135, and 207 in the Lactococcus lactis DHAD (SEQ ID NO: 232).
  • the exact positions of the three conserved cysteines in other protein sequences correspond to these positions in the S. mutans or the L. lactis amino acid sequence.
  • One skilled in the art will readily be able to identify the presence or absence of each of the three conserved cysteines in the amino acid sequence of a DHAD protein using pairwise or multiple sequence alignments.
  • other methods may be used to determine the presence of the three conserved cysteines, such as analysis by eye.
  • the DHAD Profile HMM matching proteins that have two but not the third (position 56) conserved cysteine include [4Fe-4S] DHADs and phosphogluconate dehydratases (EDDs). Proteins having the three conserved cysteines include arabonate dehydratases and [2Fe-2S] DHADs, and are members of a [2Fe-2S] DHAD/aldonic acid dehydratase group.
  • the [2Fe-2S] DHADs may be distinguished from the aldonic acid dehydratases by analyzing for signature conserved amino acids found to be present in the [2Fe-2S] DHADs or in the aldonic acid dehydratases at positions corresponding to the following positions in the Streptococcus mutans DHAD amino acid sequence.
  • signature amino acids are in [2Fe-2S] DHADs or in aldonic acid dehydratases, respectively, at the following positions (with greater than 90% occurrence): 88 asparagine vs glutamic acid; 113 not conserved vs glutamic acid; 142 arginine or asparagine vs not conserved; 165: not conserved vs glycine; 208 asparagine vs not conserved; 454 leucine vs not conserved; 477 phenylalanine or tyrosine vs not conserved; and 487 glycine vs not conserved.
  • sequence databases are queried with a Profile HMM as described herein.
  • Suitable sequence databases are known to those skilled in the art and include but are not limited to the Genbank non-redundant protein database, the SwissProt database, or UniProt database or other available databases such as GQPat (GenomeQuest, Westboro, Mass.) and BRENDA (Biobase, Beverly, Mass.).
  • bacterial [2Fe-2S] DHADs may readily be identifiable by the natural source organism being a type of bacteria. Any bacterial [2Fe-2S] DHAD identifiable by this method may be suitable for heterologous expression in a microbial host cell. It will also be appreciated that any bacterial [2Fe-2S] DHAD expressly disclosed herein by sequence may be suitable for heterologous expression in bacterial cells. Preferred bacterial [2Fe-2S] DHAD enzymes can be expressed in a host cell and provide DHAD activity.
  • Example 11 A subsequent analysis described in Example 11 returned 268 different bacterial [2Fe-2S] DHADs. Amino acid and coding sequences that were not identical to any of the 193 bacterial [2Fe-2S] DHADs provided by the initial identification are included in the sequence listing, with SEQ ID NOs listed in Table 2b.
  • Any [2Fe-2S] DHAD protein matching a sequence identifiable through the methods disclosed herein or a sequence expressly disclosed herein with an identity of at least about 95%, 96%, 97%, 98%, or 99% is a [2Fe-2S] DHAD that may be used for heterologous expression in bacterial cells as disclosed herein.
  • bacterial [2Fe-2S] DHADs expressly disclosed herein there is 100% conservation of the signature amino acids at positions: 88 aspartic acid, 142 arginine or asparagine, 208 asparagine, and 454 leucine.
  • bacterial [2Fe-2S] DHADs that may be used in the present invention are identifiable by their position in the [2Fe-2S] DHAD branch of a phylogenetic tree of DHAD related proteins such as that shown in FIG. 2 and described in Example 1.
  • bacterial [2Fe-2S] DHADs that may be used are identifiable using sequence comparisons with any of the 281 bacterial [2Fe-2S] DHADs whose sequences are provided herein, where sequence identity may be at least about 80%-85%, 85%-90%, 90%-95% or 95%-99%.
  • sequences of [2Fe-2S] DHADs may be used to identify other homologs in nature.
  • each of the DHAD encoding nucleic acid fragments described herein may be used to isolate genes encoding homologous proteins. Isolation of homologous genes using sequence-dependent protocols is well known in the art. Examples of sequence-dependent protocols include, but are not limited to: 1.) methods of nucleic acid hybridization; 2.) methods of DNA and RNA amplification, as exemplified by various uses of nucleic acid amplification technologies [e.g., polymerase chain reaction (PCR), Mullis et al., U.S. Pat. No. 4,683,202; ligase chain reaction (LCR), Tabor, S.
  • PCR polymerase chain reaction
  • LCR ligase chain reaction
  • genes encoding similar proteins or polypeptides to the [2Fe-2S] DHAD encoding genes provided herein could be isolated directly by using all or a portion of the instant nucleic acid fragments as DNA hybridization probes to screen libraries from any desired organism using methodology well known to those skilled in the art.
  • Specific oligonucleotide probes based upon the disclosed nucleic acid sequences can be designed and synthesized by methods known in the art (Maniatis, supra).
  • the entire sequences can be used directly to synthesize DNA probes by methods known to the skilled artisan (e.g., random primers DNA labeling, nick translation or end-labeling techniques), or RNA probes using available in vitro transcription systems.
  • primers can be designed and used to amplify a part of (or full-length of) the instant sequences.
  • the resulting amplification products can be labeled directly during amplification reactions or labeled after amplification reactions, and used as probes to isolate full-length DNA fragments by hybridization under conditions of appropriate stringency.
  • the primers typically have different sequences and are not complementary to each other.
  • the sequences of the primers should be designed to provide for both efficient and faithful replication of the target nucleic acid.
  • polymerase chain reaction protocols to amplify longer nucleic acid fragments encoding homologous genes from DNA or RNA.
  • the polymerase chain reaction may also be performed on a library of cloned nucleic acid fragments wherein the sequence of one primer is derived from the described nucleic acid fragments, and the sequence of the other primer takes advantage of the presence of the polyadenylic acid tracts to the 3′ end of the mRNA precursor encoding microbial genes.
  • the second primer sequence may be based upon sequences derived from the cloning vector.
  • the skilled artisan can follow the RACE protocol (Frohman et al., PNAS USA 85:8998 (1988)) to generate cDNAs by using PCR to amplify copies of the region between a single point in the transcript and the 3′ or 5′ end. Primers oriented in the 3′ and 5′ directions can be designed from the instant sequences.
  • 3′ RACE or 5′ RACE systems e.g., BRL, Gaithersburg, Md.
  • specific 3′ or 5′ cDNA fragments can be isolated (Ohara et al., PNAS USA 86:5673 (1989); Loh et al., Science 243:217 (1989)).
  • the provided [2Fe-2S] DHAD encoding sequences may be employed as hybridization reagents for the identification of homologs.
  • the basic components of a nucleic acid hybridization test include a probe, a sample suspected of containing the gene or gene fragment of interest, and a specific hybridization method. Probes are typically single-stranded nucleic acid sequences that are complementary to the nucleic acid sequences to be detected. Probes are “hybridizable” to the nucleic acid sequence to be detected.
  • the probe length can vary from 5 bases to tens of thousands of bases, and will depend upon the specific test to be done. Typically a probe length of about 15 bases to about 30 bases is suitable.
  • probe molecule Only part of the probe molecule need be complementary to the nucleic acid sequence to be detected. In addition, the complementarity between the probe and the target sequence need not be perfect. Hybridization does occur between imperfectly complementary molecules with the result that a certain fraction of the bases in the hybridized region are not paired with the proper complementary base.
  • Hybridization methods are well defined.
  • the probe and sample must be mixed under conditions that will permit nucleic acid hybridization. This involves contacting the probe and sample in the presence of an inorganic or organic salt under the proper concentration and temperature conditions.
  • the probe and sample nucleic acids must be in contact for a long enough time that any possible hybridization between the probe and sample nucleic acid may occur.
  • the concentration of probe or target in the mixture will determine the time necessary for hybridization to occur. The higher the probe or target concentration, the shorter the hybridization incubation time needed.
  • a chaotropic agent may be added. The chaotropic agent stabilizes nucleic acids by inhibiting nuclease activity.
  • chaotropic agent allows sensitive and stringent hybridization of short oligonucleotide probes at room temperature (Van Ness and Chen, Nucl. Acids Res. 19:5143-5151 (1991)).
  • Suitable chaotropic agents include guanidinium chloride, guanidinium thiocyanate, sodium thiocyanate, lithium tetrachloroacetate, sodium perchlorate, rubidium tetrachloroacetate, potassium iodide and cesium trifluoroacetate, among others.
  • the chaotropic agent will be present at a final concentration of about 3 M. If desired, one can add formamide to the hybridization mixture, typically 30-50% (v/v).
  • hybridization solutions can be employed. Typically, these comprise from about 20 to 60% volume, preferably 30%, of a polar organic solvent.
  • a common hybridization solution employs about 30-50% v/v formamide, about 0.15 to 1 M sodium chloride, about 0.05 to 0.1 M buffers (e.g., sodium citrate, Tris-HCl, PIPES or HEPES (pH range about 6-9)), about 0.05 to 0.2% detergent (e.g., sodium dodecylsulfate), or between 0.5-20 mM EDTA, FICOLL (Pharmacia Inc.) (about 300-500 kdal), polyvinylpyrrolidone (about 250-500 kdal) and serum albumin.
  • buffers e.g., sodium citrate, Tris-HCl, PIPES or HEPES (pH range about 6-9)
  • detergent e.g., sodium dodecylsulfate
  • FICOLL Fracia Inc.
  • unlabeled carrier nucleic acids from about 0.1 to 5 mg/mL, fragmented nucleic DNA (e.g., calf thymus or salmon sperm DNA, or yeast RNA), and optionally from about 0.5 to 2% wt/vol glycine.
  • Other additives may also be included, such as volume exclusion agents that include a variety of polar water-soluble or swellable agents (e.g., polyethylene glycol), anionic polymers (e.g., polyacrylate or polymethylacrylate) and anionic saccharidic polymers (e.g., dextran sulfate).
  • Nucleic acid hybridization is adaptable to a variety of assay formats. One of the most suitable is the sandwich assay format. The sandwich assay is particularly adaptable to hybridization under non-denaturing conditions.
  • a primary component of a sandwich-type assay is a solid support. The solid support has adsorbed to it or covalently coupled to it immobilized nucleic acid probe that is unlabeled and complementary to one portion of the sequence.
  • a heterologous [2Fe-2S] DHAD provides DHAD activity when expressed in a microbial cell.
  • Any [2Fe-2S] DHAD which may be identified as described herein, may be expressed in a heterologous microbial cell. Expression of any of these proteins provides DHAD activity for a biosynthetic pathway that includes conversion of 2,3-dihydroxyisovalerate to ⁇ -ketoisovalerate or 2,3-dihydroxymethylvalerate to ⁇ -ketomethylvalerate.
  • Expression of a [2Fe-2S] DHAD as opposed to a 4Fe-4D DHAD, lowers the requirement for Fe and S in clusters to obtain enzyme activity. In addition, the S.
  • mutans [ 2Fe-2S] DHAD was shown herein to have higher stability in air as compared to the sensitivity in air of the E. coli [ 4Fe-4S] DHAD, which is desirable for obtaining better activity in a heterologous host cell.
  • Bacterial cells that may be hosts for expression of a heterologous bacterial [2Fe-2S] DHAD include, but are not limited to, Clostridium, Zymomonas, Escherichia, Salmonella, Rhodococcus, Pseudomonas, Bacillus, Lactobacillus, Enterococcus, Pediococcus, Alcaligenes, Klebsiella, Paenibacillus, Arthrobacter, Corynebacterium , and Brevibacterium, Lactococcus, Leuconostoc, Oenococcus, Pediococcus , and Streptococcus .
  • Engineering expression of a heterologous bacterial [2Fe-2S] DHAD may increase DHAD activity in a host bacterial cell that naturally expresses a [2Fe-2S] DHAD or a [4Fe-4S] DHAD.
  • host cells may include, for example, E. coli and Bacillus subtilis .
  • engineering expression of a heterologous bacterial [2Fe-2S] DHAD provides DHAD activity in a host bacterial cell that has no endogenous DHAD activity.
  • Such host cells may include, for example, Lactobacillus, Enterococcus, Pediococcus and Leuconostoc.
  • Specific hosts include: Escherichia coli, Alcaligenes eutrophus, Bacillus licheniformis, Paenibacillus macerans, Rhodococcus erythropolis, Pseudomonas putida, Lactobacillus plantarum, Enterococcus faecium, Enterococcus gallinarium, Enterococcus faecalis , and Bacillus subtilis.
  • a host bacterial cell may be engineered to express a heterologous bacterial [2Fe-2S] DHAD by methods well known to one skilled in the art.
  • the coding region for the DHAD to be expressed may be codon optimized for the target host cell, as well known to one skilled in the art.
  • Vectors useful for the transformation of a variety of host cells are common and commercially available from companies such as EPICENTRE® (Madison, Wis.), Invitrogen Corp. (Carlsbad, Calif.), Stratagene (La Jolla, Calif.), and New England Biolabs, Inc. (Beverly, Mass.).
  • the vector contains a selectable marker and sequences allowing autonomous replication or chromosomal integration in the desired host.
  • suitable vectors comprise a promoter region which harbors transcriptional initiation controls and a transcriptional termination control region, between which a coding region DNA fragment may be inserted, to provide expression of the inserted coding region.
  • Both control regions may be derived from genes homologous to the transformed host cell, although it is to be understood that such control regions may also be derived from genes that are not native to the specific species chosen as a production host.
  • Initiation control regions or promoters which are useful to drive expression of bacterial [2Fe-2S] DHAD coding regions in the desired bacterial host cell are numerous and familiar to those skilled in the art.
  • Virtually any promoter capable of driving these genetic elements is suitable for the present invention including, but not limited to, lac, ara, tet, trp, IP L , IP R , T7, tac, and trc promoters (useful for expression in Escherichia coli, Alcaligenes , and Pseudomonas ); the amy, apr, and npr promoters, and various phage promoters useful for expression in Bacillus subtilis, Bacillus licheniformis , and Paenibacillus macerans ; nisA (useful for expression Gram-positive bacteria, Eichenbaum et al.
  • Termination control regions may also be derived from various genes native to the preferred hosts. Optionally, a termination site may be unnecessary; however, it is most preferred if included.
  • Certain vectors are capable of replicating in a broad range of host bacteria and can be transferred by conjugation.
  • the complete and annotated sequence of pRK404 and three related vectors: pRK437, pRK442, and pRK442(H), are available. These derivatives have proven to be valuable tools for genetic manipulation in Gram-negative bacteria (Scott et al., Plasmid 50(1):74-79 (2003)).
  • Several plasmid derivatives of broad-host-range Inc P4 plasmid RSF1010 are also available with promoters that can function in a range of Gram-negative bacteria.
  • Plasmid pAYC36 and pAYC37 have active promoters along with multiple cloning sites to allow for heterologous gene expression in Gram-negative bacteria.
  • Some vectors that are useful for transformation of Bacillus subtilis and Lactobacillus include pAM ⁇ 1 and derivatives thereof (Renault et al., Gene 183:175-182 (1996); and O′Sullivan et al., Gene 137:227-231 (1993)); pMBB1 and pHW800, a derivative of pMBB1 (Wyckoff et al. Appl. Environ. Microbiol. 62:1481-1486 (1996)); pMG1, a conjugative plasmid (Tanimoto et al., J.
  • thermosensitive variant of the broad-host-range replicon pWV101 has been modified to construct a plasmid pVE6002 which can be used to effect gene replacement in a range of Gram-positive bacteria (Maguin et al., J. Bacteriol. 174(17):5633-5638 (1992)).
  • in vitro transposomes are available from commercial sources such as EPICENTRE® to create random mutations in a variety of genomes.
  • Yeast cells that may be hosts for expression of a heterologous bacterial [2Fe-2S] DHAD are any yeast cells that are amenable to genetic manipulation and include, but are not limited to, Saccharomyces, Schizosaccharomyces, Hansenula, Candida, Kluyveromyces, Yarrowia and Pichia .
  • Suitable strains include, but are not limited to, Saccharomyces cerevisiae, Schizosaccharomyces pombe, Kluyveromyces lactis, Kluyveromyces thermotolerans, Candida glabrata, Candida albicans, Pichia stipitis and Yarrowia lipolytica . Most suitable is Saccharomyces cerevisiae.
  • Expression is achieved by transforming with a gene comprising a sequence encoding any of these [2Fe-2S] DHADs.
  • the coding region for the DHAD to be expressed may be codon optimized for the target host cell, as well known to one skilled in the art.
  • Methods for gene expression in yeast are known in the art (see for example Methods in Enzymology , Volume 194 , Guide to Yeast Genetics and Molecular and Cell Biology (Part A, 2004, Christine Guthrie and Gerald R. Fink (Eds.), Elsevier Academic Press, San Diego, Calif.). Expression of genes in yeast typically requires a promoter, operably linked to a coding region of interest, and a transcriptional terminator.
  • yeast promoters can be used in constructing expression cassettes for genes in yeast, including, but not limited to promoters derived from the following genes: CYC1, HIS3, GAL1, GAL10, ADH1, PGK, PHO5, GAPDH, ADC1, TRP1, URA3, LEU2, ENO, TPI, CUP1, FBA, GPD, GPM, and AOX1.
  • Suitable transcriptional terminators include, but are not limited to FBAt, GPDt, GPMt, ERG10t, GAL1t, CYC1, and ADH1.
  • Suitable promoters, transcriptional terminators, and [2Fe-2S] DHAD coding regions may be cloned into E. coli -yeast shuttle vectors, and transformed into yeast cells. These vectors allow strain propagation in both E. coli and yeast strains. Typically the vector used contains a selectable marker and sequences allowing autonomous replication or chromosomal integration in the desired host. Typically used plasmids in yeast are shuttle vectors pRS423, pRS424, pRS425, and pRS426 (American Type Culture Collection, Rockville, Md.), which contain an E. coli replication origin (e.g., pMB1), a yeast 2 ⁇ origin of replication, and a marker for nutritional selection.
  • E. coli replication origin e.g., pMB1
  • yeast 2 ⁇ origin of replication e.g., a yeast 2 ⁇ origin of replication
  • the selection markers for these four vectors are His3 (vector pRS423), Trp1 (vector pRS424), Leu2 (vector pRS425) and Ura3 (vector pRS426).
  • Construction of expression vectors with a chimeric gene encoding the described DHADs may be performed by either standard molecular cloning techniques in E. coli or by the gap repair recombination method in yeast.
  • the gap repair cloning approach takes advantage of the highly efficient homologous recombination in yeast.
  • a yeast vector DNA is digested (e.g., in its multiple cloning site) to create a “gap” in its sequence.
  • a number of insert DNAs of interest are generated that contain a 21 by sequence at both the 5′ and the 3′ ends that sequentially overlap with each other, and with the 5′ and 3′ terminus of the vector DNA.
  • a yeast promoter and a yeast terminator are selected for the expression cassette.
  • the promoter and terminator are amplified from the yeast genomic DNA, and Gene X is either PCR amplified from its source organism or obtained from a cloning vector comprising Gene X sequence. There is at least a 21 by overlapping sequence between the 5′ end of the linearized vector and the promoter sequence, between the promoter and Gene X, between Gene X and the terminator sequence, and between the terminator and the 3′ end of the linearized vector.
  • the “gapped” vector and the insert DNAs are then co-transformed into a yeast strain and plated on the medium containing the appropriate compound mixtures that allow complementation of the nutritional selection markers on the plasmids.
  • the presence of correct insert combinations can be confirmed by PCR mapping using plasmid DNA prepared from the selected cells.
  • the plasmid DNA isolated from yeast (usually low in concentration) can then be transformed into an E. coli strain, e.g. TOP10, followed by mini preps and restriction mapping to further verify the plasmid construct. Finally the construct can be verified
  • a cassette containing a coding region plus control elements (promoter and terminator) and auxotrophic marker is PCR-amplified with a high-fidelity DNA polymerase using primers that hybridize to the cassette and contain 40-70 base pairs of sequence homology to the regions 5′ and 3′ of the genomic area where insertion is desired.
  • the PCR product is then transformed into yeast and plated on medium containing the appropriate compound mixtures that allow selection for the integrated auxotrophic marker.
  • the promoter-coding regionX-terminator construct is PCR amplified from a plasmid DNA construct and joined to an autotrophic marker (such as URA3) by either SOE PCR or by common restriction digests and cloning.
  • the full cassette, containing the promoter-coding regionX-terminator-URA3 region, is PCR amplified with primer sequences that contain 40-70 by of homology to the regions 5′ and 3′ of location “Y” on the yeast chromosome.
  • the PCR product is transformed into yeast and selected on growth media lacking uracil. Transformants can be verified either by colony PCR or by direct sequencing of chromosomal DNA.
  • DHAD activity in a cell engineered to express a bacterial [2Fe-2S] DHAD can be confirmed using methods known in the art.
  • crude extracts from cells engineered to express a bacterial [2Fe-2S] DHAD may be used in a DHAD assay as described by Flint and Emptage (J. Biol. Chem. (1988) 263(8): 3558-64) using dinitrophenylhydrazine.
  • DHAD activity may be assayed by expressing a bacterial DHAD identifiable by the methods disclosed herein in a yeast strain that lacks endogenous DHAD activity.
  • DHAD activity may also be confirmed by more indirect methods, such as by assaying for a downstream product in a pathway requiring DHAD activity. Any product that has ⁇ -ketoisovalerate or ⁇ -ketomethylvalerate as a pathway intermediate may be measured as an assay for DHAD activity.
  • a list of such products includes, but is not limited to, valine, isoleucine, leucine, pantothenic acid, 2-methyl-1-butanol, 3-methyl-1-butanol and isobutanol.
  • Expression of a bacterial [2Fe-2S] DHAD in bacteria or yeast provides the transformed, recombinant host cell with dihydroxy-acid dehydratase activity for conversion of 2,3-dihydroxyisovalerate to ⁇ -ketoisovalerate or 2,3-dihydroxymethylvalerate to ⁇ -ketomethylvalerate.
  • Any product that has ⁇ -ketoisovalerate or ⁇ -ketomethylvalerate as a pathway intermediate may be produced with greater effectiveness in a bacterial or yeast strain disclosed herein having the described heterologous [2Fe-2S] DHAD.
  • a list of such products includes, but is not limited to, valine, isoleucine, leucine, pantothenic acid, 2-methyl-1-butanol, 3-methyl-1-butanol and isobutanol.
  • yeast biosynthesis of valine includes steps of acetolactate conversion to 2,3-dihydroxy-isovalerate by acetohydroxyacid reductoisomerase (ILV5), conversion of 2,3-dihydroxy-isovalerate to ⁇ -ketoisovalerate (also called 2-keto-isovalerate) by dihydroxy-acid dehydratase, and conversion of ⁇ -ketoisovalerate to valine by branched-chain amino acid transaminase (BAT2) and branched-chain amino acid aminotransferase (BAT1).
  • IMV5 acetohydroxyacid reductoisomerase
  • BAT2 branched-chain amino acid transaminase
  • BAT1 branched-chain amino acid aminotransferase
  • Biosynthesis of leucine includes the same steps to ⁇ -ketoisovalerate, followed by conversion of ⁇ -ketoisovalerate to alpha-isopropylmalate by alpha-isopropylmalate synthase (LEU9, LEU4), conversion of alpha-isopropylmalate to beta-isopropylmalate by isopropylmalate isomerase (LEU1), conversion of beta-isopropylmalate to alpha-ketoisocaproate by beta-IPM dehydrogenase (LEU2), and finally conversion of alpha-ketoisocaproate to leucine by branched-chain amino acid transaminase (BAT2) and branched-chain amino acid aminotransferase (BAT1).
  • BAT2 branched-chain amino acid transaminase
  • BAT1 branched-chain amino acid aminotransferase
  • the bacterial pathway is similar, involving differently named proteins and genes. Increased conversion of 2,3-dihydroxy-isovalerate to ⁇ -ketoisovalerate will increase flow in these pathways, particularly if one or more additional enzymes of a pathway is overexpressed. Thus it is desired for production of valine or leucine to use a strain disclosed herein.
  • Biosynthesis of pantothenic acid includes a step performed by DHAD, as well as steps performed by ketopantoate hydroxymethyltransferase and pantothenate synthase. Engineering of expression of these enzymes for enhanced production of pantothenic acid biosynthesis in microorganisms is described in U.S. Pat. No. 6,177,264.
  • the ⁇ -ketoisovalerate product of DHAD is an intermediate in isobutanol biosynthetic pathways disclosed in commonly owned and co-pending US Patent Publication 20070092957 A1, which is herein incorporated by reference.
  • a diagram of the disclosed isobutanol biosynthetic pathways is provided in FIG. 3 .
  • Production of isobutanol in a strain disclosed herein benefits from increased DHAD activity.
  • DHAD activity is provided by expression of a bacterial [2Fe-2S] DHAD in a bacterial or yeast cell.
  • steps in an example isobutanol biosynthetic pathway include conversion of:
  • acetolactate to 2,3-dihydroxyisovalerate see FIG. 1 , pathway step b therein as catalyzed for example by acetohydroxy acid isomeroreductase;
  • ⁇ -ketoisovalerate to isobutyraldehyde see FIG. 1 , pathway step d therein as catalyzed for example by branched-chain ⁇ -keto acid decarboxylase;
  • isobutyraldehyde to isobutanol (see FIG. 1 , pathway step e therein) as catalyzed for example by branched-chain alcohol dehydrogenase.
  • high activity KARIs disclosed therein are those from Vibrio cholerae (DNA: SEQ ID NO:389; protein SEQ ID NO:390), Pseudomonas aeruginosa PAO1, (DNA: SEQ ID NO: 422; protein SEQ ID NO:423), and Pseudomonas fluorescens PF5 (DNA: SEQ ID NO:391; protein SEQ ID NO:392).
  • Recombinant bacteria or yeast hosts disclosed herein are grown in fermentation media which contains suitable carbon substrates.
  • Additional carbon substrates may include but are not limited to monosaccharides such as fructose, oligosaccharides such as lactose maltose, galactose, or sucrose, polysaccharides such as starch or cellulose or mixtures thereof and unpurified mixtures from renewable feedstocks such as cheese whey permeate, cornsteep liquor, sugar beet molasses, and barley malt.
  • Other carbon substrates may include ethanol, lactate, succinate, or glycerol.
  • the carbon substrate may also be one-carbon substrates such as carbon dioxide, or methanol for which metabolic conversion into key biochemical intermediates has been demonstrated.
  • methylotrophic organisms are also known to utilize a number of other carbon containing compounds such as methylamine, glucosamine and a variety of amino acids for metabolic activity.
  • methylotrophic yeasts are known to utilize the carbon from methylamine to form trehalose or glycerol (Bellion et al., Microb. Growth C 1 Compd ., [Int. Symp.], 7th (1993), 415-32, Editor(s): Murrell, J. Collin; Kelly, Don P. Publisher: Intercept, Andover, UK).
  • Candida will metabolize alanine or oleic acid (Sulter et al., Arch. Microbiol. 153:485-489 (1990)).
  • source of carbon utilized in the present invention may encompass a wide variety of carbon containing substrates and will only be limited by the choice of organism.
  • preferred carbon substrates are glucose, fructose, and sucrose, or mixtures of these with C5 sugars such as xylose and/or arabinose for yeasts cells modified to use C5 sugars.
  • Sucrose may be derived from renewable sugar sources such as sugar cane, sugar beets, cassaya, sweet sorghum, and mixtures thereof.
  • Glucose and dextrose may be derived from renewable grain sources through saccharification of starch based feedstocks including grains such as corn, wheat, rye, barley, oats, and mixtures thereof.
  • fermentable sugars may be derived from renewable cellulosic or lignocellulosic biomass through processes of pretreatment and saccharification, as described, for example, in co-owned and co-pending U.S. Patent Application Publication No. 2007/0031918A1, which is herein incorporated by reference.
  • Biomass refers to any cellulosic or lignocellulosic material and includes materials comprising cellulose, and optionally further comprising hemicellulose, lignin, starch, oligosaccharides and/or monosaccharides. Biomass may also comprise additional components, such as protein and/or lipid.
  • Biomass may be derived from a single source, or biomass can comprise a mixture derived from more than one source; for example, biomass may comprise a mixture of corn cobs and corn stover, or a mixture of grass and leaves.
  • Biomass includes, but is not limited to, bioenergy crops, agricultural residues, municipal solid waste, industrial solid waste, sludge from paper manufacture, yard waste, wood and forestry waste.
  • biomass examples include, but are not limited to, corn grain, corn cobs, crop residues such as corn husks, corn stover, grasses, wheat, wheat straw, barley, barley straw, hay, rice straw, switchgrass, waste paper, sugar cane bagasse, sorghum, soy, components obtained from milling of grains, trees, branches, roots, leaves, wood chips, sawdust, shrubs and bushes, vegetables, fruits, flowers, animal manure, and mixtures thereof.
  • crop residues such as corn husks, corn stover, grasses, wheat, wheat straw, barley, barley straw, hay, rice straw, switchgrass, waste paper, sugar cane bagasse, sorghum, soy, components obtained from milling of grains, trees, branches, roots, leaves, wood chips, sawdust, shrubs and bushes, vegetables, fruits, flowers, animal manure, and mixtures thereof.
  • fermentation media In addition to an appropriate carbon source, fermentation media must contain suitable minerals, salts, cofactors, buffers and other components, known to those skilled in the art, suitable for the growth of the cultures and promotion of an enzymatic pathway comprising a bacterial [2Fe-2S] DHAD.
  • Suitable growth media in the present invention are common commercially prepared media such as Luria Bertani (LB) broth, Sabouraud Dextrose (SD) broth, Yeast Medium (YM) broth, or broth that includes yeast nitrogen base, ammonium sulfate, and dextrose (as the carbon/energy source) or YPD Medium, a blend of peptone, yeast extract, and dextrose in optimal proportions for growing most Saccharomyces cerevisiae strains.
  • Other defined or synthetic growth media may also be used, and the appropriate medium for growth of the particular microorganism will be known by one skilled in the art of microbiology or fermentation science.
  • agents known to modulate catabolite repression directly or indirectly e.g., cyclic adenosine 2′:3′-monophosphate, may also be incorporated into the fermentation medium.
  • Suitable pH ranges for the fermentation of yeast are typically between pH 3.0 to pH 9.0. where pH 5.0 to pH 8.0 is preferred as the initial condition.
  • Suitable pH ranges for the fermentation of other microorganisms are between pH 3.0 to pH 7.5, where pH 4.5.0 to pH 6.5 is preferred as the initial condition.
  • Fermentations may be performed under aerobic or anaerobic conditions, where anaerobic or microaerobic conditions are preferred.
  • Fermentation may be a batch method of fermentation.
  • a classical batch fermentation is a closed system where the composition of the medium is set at the beginning of the fermentation and not subject to artificial alterations during the fermentation. Thus, at the beginning of the fermentation the medium is inoculated with the desired organism or organisms, and fermentation is permitted to occur without adding anything to the system.
  • “batch” fermentation is batch with respect to the addition of carbon source and attempts are often made at controlling factors such as pH and oxygen concentration.
  • the metabolite and biomass compositions of the system change constantly up to the time the fermentation is stopped.
  • cells moderate through a static lag phase to a high growth log phase and finally to a stationary phase where growth rate is diminished or halted. If untreated, cells in the stationary phase will eventually die.
  • Cells in log phase generally are responsible for the bulk of production of end product or intermediate.
  • a variation on the standard batch system is the fed-batch system.
  • Fed-batch fermentation processes are also suitable in the present invention and comprise a typical batch system with the exception that the substrate is added in increments as the fermentation progresses.
  • Fed-batch systems are useful when catabolite repression is apt to inhibit the metabolism of the cells and where it is desirable to have limited amounts of substrate in the media. Measurement of the actual substrate concentration in fed-batch systems is difficult and is therefore estimated on the basis of the changes of measurable factors such as pH, dissolved oxygen and the partial pressure of waste gases such as CO2. Batch and fed-batch fermentations are common and well known in the art and examples may be found in Thomas D.
  • the fermentation culture may be adapted to continuous fermentation methods.
  • Continuous fermentation is an open system where a defined fermentation medium is added continuously to a bioreactor and an equal amount of conditioned media is removed simultaneously for processing.
  • Continuous fermentation generally maintains the cultures at a constant high density.
  • Continuous fermentation allows for the modulation of one factor or any number of factors that affect cell growth or end product concentration.
  • one method will maintain a limiting nutrient such as the carbon source or nitrogen level at a fixed rate and allow all other parameters to moderate.
  • a number of factors affecting growth can be altered continuously while the cell concentration, measured by the turbidity of the culture medium, is kept constant.
  • Continuous systems strive to maintain steady state growth conditions and thus the cell loss due to the medium being drawn off must be balanced against the cell growth rate in the fermentation.
  • batch, fed-batch, continuous processes, or any known mode of fermentation is suitable for growth of the described recombinant microbial host cell.
  • cells may be immobilized on a substrate as whole cell catalysts and subjected to fermentation conditions for isobutanol production.
  • Bioproduced isobutanol may be isolated from the fermentation medium using methods known in the art such as for ABE fermentations (see for example, Durre, Appl. Microbiol. Biotechnol. 49:639-648 (1998), Groot et al., Process Biochem. 27:61-75 (1992), and references therein).
  • solids may be removed from the fermentation medium by centrifugation, filtration, decantation, or the like.
  • the isobutanol may be isolated from the fermentation medium using methods such as distillation, azeotropic distillation, liquid-liquid extraction, adsorption, gas stripping, membrane evaporation, or pervaporation.
  • distillation can be used to separate the mixture up to its azeotropic composition. Distillation may be used in combination with another separation method to obtain separation around the azeotrope. Methods that may be used in combination with distillation to isolate and purify butanol include, but are not limited to, decantation, liquid-liquid extraction, adsorption, and membrane-based techniques. Additionally, butanol may be isolated using azeotropic distillation using an entrainer (see for example Doherty and Malone, Conceptual Design of Distillation Systems , McGraw Hill, New York, 2001).
  • the butanol-water mixture forms a heterogeneous azeotrope so that distillation may be used in combination with decantation to isolate and purify the isobutanol.
  • the isobutanol containing fermentation broth is distilled to near the azeotropic composition.
  • the azeotropic mixture is condensed, and the isobutanol is separated from the fermentation medium by decantation.
  • the decanted aqueous phase may be returned to the first distillation column as reflux.
  • the isobutanol-rich decanted organic phase may be further purified by distillation in a second distillation column.
  • the isobutanol may also be isolated from the fermentation medium using liquid-liquid extraction in combination with distillation.
  • the isobutanol is extracted from the fermentation broth using liquid-liquid extraction with a suitable solvent.
  • the isobutanol-containing organic phase is then distilled to separate the butanol from the solvent.
  • Distillation in combination with adsorption may also be used to isolate isobutanol from the fermentation medium.
  • the fermentation broth containing the isobutanol is distilled to near the azeotropic composition and then the remaining water is removed by use of an adsorbent, such as molecular sieves (Aden et al. Lignocellulosic Biomass to Ethanol Process Design and Economics Utilizing Co - Current Dilute Acid Prehydrolysis and Enzymatic Hydrolysis for Corn Stover , Report NREL/TP-510-32438, National Renewable Energy Laboratory, June 2002).
  • distillation in combination with pervaporation may be used to isolate and purify the isobutanol from the fermentation medium.
  • the fermentation broth containing the isobutanol is distilled to near the azeotropic composition, and then the remaining water is removed by pervaporation through a hydrophilic membrane (Guo et al., J. Membr. Sci. 245, 199-210 (2004)).
  • Microbial strains were obtained from The American Type Culture Collection (ATCC), Manassas, Va., unless otherwise noted.
  • ATCC American Type Culture Collection
  • the oligonucleotide primers used in the following Examples were synthesized by Sigma-Genosys (Woodlands, Tex.) or Integrated DNA Technologies (Coralsville, Iowa).
  • HPLC high performance liquid chromatography
  • Shodex SH-1011 column with a Shodex SH-G guard column both available from Waters Corporation, Milford, Mass.
  • RI refractive index
  • Chromatographic separation is achieved using 0.01 M H 2 SO 4 as the mobile phase with a flow rate of 0.5 mL/min and a column temperature of 50° C.
  • Isobutanol retention time is about 47.6 minutes.
  • DHADs dihydroxy-acid dehydratases
  • Sequences were selected from the search results based on E value cutoff of 10 ⁇ 5 with removal of 95% identity sequences. Sequences that were shorter than 350 amino acids and sequences that were longer than 650 amino acids were also removed. The resultant set of 976 amino acid sequences included dihydroxy-acid dehydratases, phosphogluconate dehydratrases, and aldonic acid dehydratases.
  • a profile HMM was generated from the experimentally verified DHADs described in Example 2. See details below on building, calibrating, and searching with this profile HMM.
  • Multiple sequence alignments of the amino acid sequences were performed with the Clustal W algorithm (Thompson, J. D., Higgins, D. G., and Gibson T. J. (1994) Nuc. Acid Res.
  • Phylogenetic trees were generated from sequence alignments based on the Neighbor Joining method. A tree representing phylogenetic relationships among the 976 sequences is shown in FIG. 2 . Four main main branches emerged from this analysis. They are labeled “4Fe-4S DHAD”, “2Fe-2S DHAD”, “aldonic acid dehydratase”, and “EDD”, based on the criteria detailed below. A fifth small branch of 17 sequences is marked as “Und” for undefined.
  • the aligned sequences were initially analyzed for the presence of three cysteines determined to be essential for enzyme activity and likely involved in Fe—S coordination in the Azospirillum brasiliense arabonate dehydratase, which was reported as a [4Fe-4S] cluster protein (Watanabe, S et al. J. Biol. Chem . (2006) 281:33521-33536).
  • Each of the 976 sequences has the cysteines corresponding to two of the Azospirillum brasiliense arabonate dehydratase essential cysteines (at positions 124 and 197).
  • a different branch of the tree contains 322 sequences, among which is the known [4Fe-4S] cluster DHAD of E. coli .
  • This 322 sequence branch is labeled in FIG. 2 as “4Fe-4S DHAD”. All sequences within this branch, and in the branch of 17 sequences (“Und”), contain glycine at the position corresponding to the third cysteine.
  • the remaining 469 sequences which are clustered in two branches and comprise both the aldonic acid recognizing A. brasiliense arabonate dehydratase and a set of DHADs, possess all three cysteines. These cysteines are at positions 56, 129, and 201 in the S.
  • mutans DHAD SEQ ID NO: 168 and at positions 61, 135, and 207 in the L. lactis DHAD (SEQ ID NO: 232). Shown in FIG. 1 are examples of regions from multiple sequence alignments that include the conserved cysteines.
  • Arabidopsis thaliana is a plant as is spinach, and the spinach DHAD has been identified as a [2Fe-2S] cluster DHAD (Flint and Emptage (1988) J. Biol. Chem. 263:3558-3564), the Arabidopsis thaliana DHAD may be a [2Fe-2S] cluster DHAD.
  • the S. solfataricus DHAD is reported to be oxygen resistant like the spinach [2Fe-2S] cluster DHAD, (Kim and Lee (2006) J. Biochem. 139, 591-596) which is an indication that the S. solfataricus DHAD may be a [2Fe-2S] cluster DHAD.
  • the 274 sequence clade is labeled on FIG. 4 as “2Fe-2S DHAD”.
  • 193 of these sequences are from bacterial sources.
  • the three conserved cysteines and the conserved residues specified in Table 4 can be identified in multiple sequence alignments of the 193 bacterial DHADs, employing the alignment procedure described above.
  • the sequences of the 193 bacterial [2Fe-2S] DHADs are provided in the sequence listing and the SEQ ID NOs are listed in Table 2a.
  • DHADs Seven bacterial DHADs that were identified as members of the [2Fe-2S] phylogenetic group were expressed in E. coli and dihydroxy-acid dehydratase activity was found as described in Example 2 below. These DHADs are from Nitrosomonas europaea (SEQ ID NO:310), Synechocystis sp. PCC6803 (SEQ ID NO: 298), Streptococcus mutans (SEQ ID NO:168), Streptococcus thermophilus (SEQ ID NO:164), Ralstonia metallidurans (SEQ ID NO:346), Ralstonia eutropha (SEQ ID NO:344), and Lactococcus lactis (SEQ ID NO:232).
  • Nitrosomonas europaea SEQ ID NO:310
  • Synechocystis sp. PCC6803 SEQ ID NO: 298
  • Streptococcus mutans SEQ ID NO:168
  • DHAD from Flavobacterium johnsoniae was found to have dihydroxy-acid dehydratase activity when expressed in E. coli .
  • the amino acid sequences of these experimentally determined functional bacterial DHADs were analyzed using the HMMER software package (The theory behind profile HMMs is described in R. Durbin, S. Eddy, A. Krogh, and G. Mitchison, Biological sequence analysis: probabilistic models of proteins and nucleic acids , Cambridge University Press, 1998; Krogh et al., 1994; J. Mol. Biol. 235:1501-1531), following the user guide which is available from HMMER (Janelia Farm Research Campus, Ashburn, Va.).
  • HMM Profile Hidden Markov Model
  • the Profile HMM was built as follows:
  • Step 1 Build a Sequence Alignment
  • the hmmbuild program was run on the set of aligned sequences using default parameters. hmmbuild reads the multiple sequence alignment file, builds a new Profile HMM, and saves the Profile HMM to file. Using this program an un-calibrated profile was generated from the multiple alignment for each set of subunit sequences described above.
  • a Profile HMM is capable of modeling gapped alignments, e.g. including insertions and deletions, which lets the software describe a complete conserved domain (rather than just a small ungapped motif). Insertions and deletions are modeled using insertion (I) states and deletion (D) states. All columns that contain more than a certain fraction x of gap characters will be assigned as an insert column. By default, x is set to 0.5. Each match state has an I and a D state associated with it. HMMER calls a group of three states (M/D/I) at the same consensus position in the alignment a “node”.
  • M and I states are emitters, while D states are silent. The transitions are arranged so that at each node, either the M state is used (and a residue is aligned and scored) or the D state is used (and no residue is aligned, resulting in a deletion-gap character, ‘-’). Insertions occur between nodes, and I states have a self-transition, allowing one or more inserted residues to occur between consensus columns.
  • the scores of residues in a match state are proportional to Log — 2 (p_x)/(null_x).
  • p_x is the probability of an amino acid residue, at a particular position in the alignment, according to the Profile HMM
  • null_x is the probability according to the Null model.
  • the Null model is a simple one state probabilistic model with pre-calculated set of emission probabilities for each of the 20 amino acids derived from the distribution of amino acids in the SWISSPROT release 24.
  • State transition scores are also calculated as log odds parameters and are proportional to Log — 2 (t_x). Where t_x is the probability of transiting to an emitter or non-emitter state.
  • the Profile HMM was read using hmmcalibrate which scores a large number of synthesized random sequences with the Profile (the default number of synthetic sequences used is 5,000), fits an extreme value distribution (EVD) to the histogram of those scores, and re-saves the HMM file now including the EVD parameters.
  • EVD extreme value distribution
  • hmmcalibrate writes two parameters into the HMM file on a line labeled “EVD”: these parameters are the ⁇ (location) and ⁇ (scale) parameters of an extreme value distribution (EVD) that best fits a histogram of scores calculated on randomly generated sequences of about the same length and residue composition as SWISS-PROT. This calibration was done once for the Profile HMM.
  • the calibrated Profile HMM for the DHAD set of sequences is provided in Table 1.
  • the Profile HMM is provided in a chart that gives the probability of each amino acid occurring at each position in the amino acid sequence. The highest probability is highlighted for each position.
  • the first line for each position reports the match emission scores: probability for each amino acid to be in that state (highest score is highlighted).
  • the second line reports the insert emission scores, and the third line reports on state transition scores: M ⁇ M, M ⁇ I, M ⁇ D; I ⁇ M, I ⁇ I; D ⁇ M, D ⁇ D; B ⁇ M; M ⁇ E.
  • the DHAD Profile HMM shows that methionine has a 1757 probability of being in the first position, the highest probability which is highlighted.
  • glutamic acid has the highest probability, which is 1356.
  • lysine has the highest probability, which is 1569.
  • the Profile HMM was evaluated using hmmsearch, which reads a Profile HMM from hmmfile and searches a sequence file for significantly similar sequence matches.
  • the sequence file searched contained 976 sequences (see above).
  • Z parameter the size of the database (Z parameter) was set to 1 billion. This size setting ensures that significant E-values against the current database will remain significant in the foreseeable future.
  • the E-value cutoff was set at 10.
  • Genomic DNA was prepared from each strain listed in Table 1 using a MasterPure DNA Purification Kit (Epicentre, Madison, Wis.).
  • the plasmid vector was amplified with primers pET28a-F (NotI) (SEQ ID NO:397) and pET28a-R (NheI) (SEQ ID NO:398) to remove the his tag region. Both gene and plasmid fragments were digested with NheI and NotI before ligation.
  • the ligation mixture was transformed into E. coli (Top 10) competent cells (Invitrogen). Transformants were grown in LB agar plates supplemented with 50 ⁇ g/ml of kanamycin.
  • Enzymatic activity of the crude extract was assayed at 37° C. as follows. Cells to be assayed for DHAD were suspended in 2-5 volumes of 50 mM Tris, 10 mM MgSO 4 , pH 8.0 (TM8) buffer, then broken by sonication at 0° C. The crude extract from the broken cells was centrifuged to pellet the cell debris. The supernatants were removed and stored on ice until assayed (initial assay was within 2 hrs of breaking the cells). It was found that the DHADs assayed herein were stable in crude extracts kept on ice for a few hours. The activity was also preserved when small samples were frozen in liquid N 2 and stored at ⁇ 80° C.
  • Protein assays were performed using the Pierce Better Bradford reagent (cat 23238) using BSA as a standard. Dilutions for protein assays were made in TM8 buffer when necessary.
  • DHADs were active when expressed in E. coli , and the specific activities are given in Table 6.
  • the DHAD from Streptococcus mutans had the highest specific activity.
  • the DHAD from S. mutans was further purified and characterized.
  • S. mutans DHAD six liters of culture of the E. coli Tuner strain harboring the pET28a plasmid with the S. mutans ilvD were grown and induced with IPTG.
  • the enzyme was purified by breaking the cells, as described in Example 2, in a 50 mM Tris buffer pH 8.0 containing 10 mM MgCl 2 (TM8 buffer), centrifuging to remove cell debris, then loading the supernatant of the crude extract on a Q Sepharose (GE Healthcare) column and eluting the DHAD with an increasing concentration of NaCl in TM8 buffer.
  • the fractions containing the DHAD based on the color appearance were pooled and loaded onto a Sephacryl S-100 (GE Healthcare) column and eluted with TM8 buffer. As judged by SDS gels, the purity of the protein eluted from the Sephacryl column was estimated to be 60-80%.
  • the activity of the partially purified enzyme was assayed at 37° C. as described by Flint et al. (J. Biol. Chem. (1988) 263(8): 3558-64).
  • the specific activity of the purified protein was 40 ⁇ mol min ⁇ 1 mg ⁇ 1 .
  • the k cat for the purified enzyme was estimated to be 50-70 sec ⁇ 1 .
  • the UV-visible spectrum of the purified S. mutans is shown in FIG. 5 .
  • the number of peaks above 300 nm is typical of proteins with [2Fe-2S] clusters.
  • the S. mutans DHAD was reduced with sodium dithionite and EPR spectra were obtained at varying temperatures.
  • FIG. 6 show spectra measured at temperatures between 20° K. and 70° K. That the EPR spectrum of S. mutans is measurable up to 70° K. is indicative that it contains a [2Fe-2S] cluster. It is well known for example that the EPR spectra of proteins containing [4Fe-4S] clusters are not observable at temperatures much above 10° K. (See, for example, Rupp, et al. Biochimica et Biophysica Acta (1978) 537:255-269.)
  • DHAD Dihydroxy-Acid Dehydratase
  • the purpose of this example is to describe how to clone and express a dihydroxy-acid dehydratase gene (ilvD) from different bacterial sources in Lactobacillus plantarum PN0512 (ATCC PTA-7727).
  • a shuttle vector pDM1 (SEQ ID NO:410) was used for cloning and expression of ilvD genes from Lactococcus lactis subsp lactis NCDO2118 (NCIMB 702118) [Godon et al., J. Bacteriol. (1992) 174:6580-6589] and Streptococcus mutans UA159 (ATCC 700610) in L. plantarum PN0512.
  • Plasmid pDM1 contains a minimal pLF1 replicon ( ⁇ 0.7 Kbp) and pemK-pemI toxin-antitoxin (TA) from Lactobacillus plantarum ATCC14917 plasmid pLF1, a P15A replicon from pACYC184, chloramphenicol marker for selection in both E. coli and L. plantarum , and P30 synthetic promoter [Rud et al, Microbiology (2006) 152:1011-1019]. Plasmid pLF1 (C.-F. Lin et al., GenBank accession no.
  • AF508808 is closely related to plasmid p256 [S ⁇ rvig et al., Microbiology (2005) 151:421-431], whose copy number was estimated to be ⁇ 5-10 copies per chromosome for L. plantarum NC7.
  • a P30 synthetic promoter was derived from L. plantarum rRNA promoters that are known to be among the strongest promoters in lactic acid bacteria (LAB) [Rud et al. Microbiology (2005) 152:1011-1019].
  • Lactococcus lactis ilvD coding region (SEQ ID NO:231) was PCR-amplified from Lactococcus lactis subsp lactis NCDO2118 genomic DNA with primers 3T-ilvDLI (BamHI) (SEQ ID NO:408) and 5B-ilvDLI (NotI) (SEQ ID NO:409).
  • L. lactis subsp lactis NCDO2118 genomic DNA was prepared with a Puregene Gentra Kit (QIAGEN, CA).
  • the 1.7 Kbp L. lactis ilvD PCR product (ilvDLI) was digested with NotI and treated with the Klenow fragment of DNA polymerase to make blunt ends. The resulting L.
  • lactis ilvD coding region fragment was digested with BamHI and gel-purified using a QIAGEN gel extraction kit (QIAGEN, CA). Plasmid pDM1 was digested with ApaLI, treated with the Klenow fragment of DNA polymerase to make blunt ends, and then digested with BamHI. The gel purified L. lactis ilvD coding region fragment was ligated into the BamHI and ApaLI (blunt) sites of the plasmid pDM1. The ligation mixture was transformed into E. coli Top10 cells (Invitrogen, CA). Transformants were plated for selection on LB chloramphenicol plates. Positive clones were screened by SalI digestion, giving one fragment with an expected size of 5.3 Kbp. The positive clones were further confirmed by DNA sequencing. The correct clone was named pDM1-ilvD ( L. lactis ).
  • the S. mutans UA159 (ATCC 700610) ilvD coding region from the plasmid pET28a was cloned on the plasmid pDM1.
  • the construction of pET28a containing the S. mutans ilvD was described in Example 2.
  • the plasmid pET28a containing the S. mutans ilvD was digested with XbaI and NotI, treated with the Klenow fragment of DNA polymerase to make blunt ends, and a 1,759 by fragment containing the S. mutans ilvD coding region was gel-purified.
  • Plasmid pDM1 was digested with BamHI, treated with the Klenow fragment of DNA polymerase to make blunt ends, and then digested with PvuII.
  • the gel purified fragment containing S. mutans ilvD coding region was ligated into the BamHI (blunt) and PvuII sites of the plasmid pDM1.
  • the ligation mixture was transformed into E. coli Top10 cells (Invitrogen, CA). Transformants were plated for selection on LB chloramphenicol plates. Positive clones were screened by ClaI digestion, giving one fragment with an expected size of 5.5 Kbp. The correct clone was named pDM1-ilvD ( S. mutans ).
  • Cells were harvested at 3700 ⁇ g for 8 min at 4° C., washed with 100 ml cold 1 mM MgCl 2 , centrifuged at 3700 ⁇ g for 8 min at 4° C., washed with 100 ml cold 30% PEG-1000 (81188, Sigma-Aldrich, St. Louis, Mo.), recentrifuged at 3700 ⁇ g for 20 min at 4° C., then resuspended in 1 ml cold 30% PEG-1000.
  • 60 ⁇ l of electro-competent cells were mixed with ⁇ 100 ng plasmid DNA in a cold 1 mm gap electroporation cuvette and electroporated in a BioRad Gene Pulser (Hercules, Calif.) at 1.7 kV, 25 ⁇ F, and 400 ⁇ .
  • Cells were resuspended in 1 ml MRS medium containing 500 mM sucrose and 100 mM MgCl 2 , incubated at 30° C. for 2 hrs, and then plated on MRS medium plates containing 10 ⁇ g/ml of chloramphenicol.
  • L. plantarum PN0512 transformants carrying pDM1-ilvD ( L. lactis ) or pDM1-ilvD ( S. mutans ). as well as control transformants with the pDM1 vector alone, were grown overnight in Lactobacilli MRS medium at 30° C. 120 ml of MRS medium supplemented with 100 mM MOPS (pH7.5), 40 ⁇ M ferric citrate, 0.5 mM L-cysteine, and 10 ⁇ g/ml chloramphenicol was inoculated with overnight culture to an OD600 0.1 in a 125 ml screw cap flask, for each overnight sample. The cultures were anaerobically incubated at 37° C.
  • the shuttle vector pRS423 FBA ilvD (Strep) (SEQ ID NO:430) was used for the expression of DHAD from Streptococcus mutans .
  • This shuttle vector contained an F1 origin of replication (1423 to 1879) for maintenance in E. coli and a 2 micron origin (nt 8082 to 9426) for replication in yeast.
  • the vector has an FBA promoter (nt 2111 to 3108; SEQ ID NO:425) and FBA terminator (nt 4861 to 5860). In addition, it carries the His marker (nt 504 to 1163) for selection in yeast and ampicillin resistance marker (nt 7092 to 7949) for selection in E. coli .
  • the ilvD coding region (nt 3116 to 4828) from Streptococcus mutans UA159 is between the FBA promoter and FBA terminator forming a chimeric gene for expression.
  • the expression vector pRS423 FBA IlvD (Strep) was transformed in combination with empty vector pRS426 into BY4741 cells (obtainable from ATCC, # 201388).
  • the transformants were grown on synthetic medium lacking histidine and uracil (Teknova). Growth on liquid medium for assay was carried out by adding 5 ml of an overnight culture into 100 ml medium in a 250 ml flask. The cultures were harvested when they reached 1 to 2 O.D. at 600 nm.
  • the samples were washed with 10 ml of 20 mM Tris (pH 7.5) and then resuspended in 1 ml of the same Tris buffer.
  • the samples were transferred into 2.0 ml tubes containing 0.1 mm silica (Lysing Matrix B, MP biomedicals).
  • the cells were then broken in a bead-beater (BIO101).
  • the supernatant was obtained by centrifugation in a microfuge at 13,000 rpm at 4° C. for 30 minutes.
  • 0.06 to 0.1 mg of crude extract protein was used in DHAD assay at 37° C. as described by Flint and Emptage (J. Biol. Chem.
  • the dehydratase from Streptococcus mutans had a specific activity of 0.24 ⁇ mol min ⁇ 1 mg ⁇ 1 when expressed in yeast.
  • a control strain containing empty vectors pRS423 and pRS426 had a background of activity in the range of 0.03 to 0.06 ⁇ mol min ⁇ 1 mg ⁇ 1 .
  • the ilvD coding region from L. lactis was amplified with the forward primer IlvD (LI)-F (SEQ ID NO:420) and reverse primer IlvD (LI)-R (SEQ ID NO:421).
  • the amplified fragment was cloned into the shuttle vector pNY13by gap repair.
  • pNY13 (SEQ ID NO:437) was derived from pRS423.
  • This shuttle vector contained an F1 origin of replication (1423 to 1879) for maintenance in E. coli and a 2 micron origin (nt 7537 to 8881) for replication in yeast.
  • the vector has an FBA promoter (nt 2111 to 3110) and FBA terminator (nt 4316 to 5315). In addition, it carries the His marker (nt 504 to 1163) for selection in yeast and Ampicillin resistance marker (nt 6547 to 7404) for selection in E. coli.
  • pRS423 FBA ilvD L. lactis
  • This construct was transformed into yeast strain BY4743 ( ⁇ LEU1) (Open Biosystems, Huntsville, Ala.; Catalog #YSC1021-666629) along with the empty vector pRS426 as described in Example 6.
  • the growth and assay of yeast strains containing the expression vector were also carried out according to the procedures as described in Example 6.
  • the dihydroxy-acid dehydratase activity in yeast strains with the L. lactis IlvD gene was determined to be in the range of 0.05 to 0.17 ⁇ mol min ⁇ 1 mg ⁇ 1 . This activity was slightly above the control. Complementation experiments were carried out to investigate the expression of this DHAD and DHADs from other bacteria (example 8).
  • the endogenous DHAD enzyme of S. cerevisiae is encoded by the ILV3 gene and the protein is targeted to the mitochondrion. Deletion of this gene results in loss of endogenous DHAD activity and provides a test strain where expression of heterologous cytosolic DHAD activity can be readily assessed. Deletion of ILV3 results in an inability of the strain to grow in the absence of branched-chained amino acids. Expression of different bacterial DHADs was assayed by determining their ability to complement the yeast ILV3 deletion strain such that it grows in the absence of branched-chained amino acids.
  • Expression shuttle vectors containing ilvD gene sequences encoding DHADs from the bacteria listed in Table 8 were constructed. The basic elements of these expression constructs were the same as the pRS423 FBA ilvD (strep) vector described in Example 6. Each of the ilvD coding regions was prepared by PCR as described in Example 2 and cloned to replace the Streptococcus mutans ilvD coding region in pRS423 FBA ilvD (Strep) creating the plasmids listed in Table 8. These expression constructs were transformed into the ILV3 deletion strain, BY4741 ilv3::URA3 and was prepared as follows.
  • An ilv3::URA3 disruption cassette was constructed by PCR amplification of the URA3 marker from pRS426 (ATCC No. 77107) with primers “ILV3::URA3 F” and “ILV3::URA3 R”, given as SEQ ID NOs: 431 and 432. These primers produced a 1.4 kb URA3 PCR product that contained 70 by 5′ and 3′ extensions identical to sequences upstream and downstream of the ILV3 chromosomal locus for homologous recombination. The PCR product was transformed into BY4741 cells (ATCC 201388) using standard genetic techniques ( Methods in Yeast Genetics, 2005, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., pp.
  • Transformants were screened by PCR using primers “ILV3 F Check” and “URA3 REV Check”, given as SEQ ID NOs:433 and 434, to verify integration at the correct site and disruption of the endogenous ILV3 locus.
  • the transformants with bacterial DHADs in Table 8 were selected on plates with yeast synthetic medium lacking histidine. Colonies selected were then patched onto plates lacking valine, leucine and isoleucine. Strains containing the expression vectors listed in Table 8 were able to grow on these plates lacking the branched chain amino acids, while the control strain with the control plasmid did not. This result indicated that DHADs from these bacteria were actively expressed in S. cerevisiae .
  • the DHAD from L. lactis was purified and characterized.
  • L. lactis DHAD 14 liters of culture of the E. coli Tuner (DE3) strain (Novagen) harboring the pET28a plasmid containing the L. lactis ilvD were grown and induced with IPTG.
  • the enzyme was purified by breaking the cells, as described in Example 2, in 120 mls of 50 mM Tris buffer pH 8.0 containing 10 mM MgCl 2 (TM8 buffer), centrifuging to remove cell debris, then loading the supernatant of the crude extract on a 5 ⁇ 15 cm Q Sepharose (GE Healthcare) column and eluting the DHAD with an increasing concentration of NaCl in TM8 buffer.
  • the fractions containing the DHAD were pooled, made 1 M in (NH 4 ) 2 SO 4 and loaded onto a 2.6 ⁇ 15 cm phenyl-Sepharose column (GE Healthcare) column equilibrated with 1 M (NH 4 ) 2 SO 4 in TM8 buffer and eluted with a decreasing gradient of (NH 4 ) 2 SO 4 .
  • the fractions containing DHAD off the phenyl-Sepharose column were pooled and concentrated to 10 ml. This was loaded onto a 3.5 ⁇ 60 cm Superdex-200 column (GE Healthcare) and eluted with TM8.
  • the fractions containing DHAD activity were pooled, concentrated, and frozen as beads in N 2(I) As judged by SDS gels, the purity of the protein eluted from the Superdex-200 column was estimated to be >80%.
  • the activity of the enzyme was assayed at 37° C. as described by Flint et al. (J. Biol. Chem. (1988) 263(8): 3558-64).
  • the specific activity of the purified protein was 64 ⁇ mol min ⁇ 1 mg ⁇ 1 at pH 8 and 37° C.
  • the k cat for the purified enzyme was 71 sec ⁇ 1 .
  • the UV-visible spectrum of the purified L. lactis is shown in FIG. 9 . It is characteristic of proteins with [2Fe-2S] clusters.
  • the first three steps of an isobutanol biosynthetic pathway are performed by the enzymes acetolactate synthase, ketol-acid reductoismerase (KARI), and dihydroxy-acid dehydratase.
  • Acetolactate synthase is encoded by alsS.
  • KARI genes are known as ILV5 in yeast or ilvC in bacteria. Once ⁇ -ketoisovalerate (KIV) is formed from pyruvate by the reaction of these three enzymes, it can be further converted to isobutanol in yeast by alcohol dehydrogenases.
  • Vector pLH532 (SEQ ID NO:411) was constructed to express KARI and alsS genes. This vector is derived from the 2 MICRON based vector pHR81. In pLH532 the alsS coding region from B. subtilis (nt 14216 to 15931) was under the control of the CUP1 promoter (nt. 15939 to 16386). There were two KARI genes in pLH532: the ilvC coding region from P. fluorescens Pf5 (nt. 10192 to 11208) was under the control of the yeast ILV5 promoter (nt. 11200 to 12390), and the yeast ILV5 coding region (nt. 8118-9167) was placed under the control of the FBA promoter (nt. 7454-8110). The selection marker was URA3 (nt. 3390 to 4190).
  • the yeast host for isobutanol production was BY4741 pdc1::FBAp-alsS-LEU2. This strain was constructed as follows. First, the expression plasmid pRS426-FBAp-alsS was constructed. The 1.7 kb alsS coding region fragment of pRS426::GPD::alsS::CYC was isolated by gel purification following BbvCI and PacI digestion.
  • This plasmid has a chimeric gene containing the GPD promoter (SEQ ID NO:439), the alsS coding region from Bacillus subtilis (SEQ ID NO:438), and the CYC1 terminator (SEQ ID NO:440) and was described in Example 17 of US Patent Publication # US20070092957A1 which is herein incorporated by reference.
  • the ILV5 fragment from plasmid pRS426::FBA::ILV5::CYC also described in US20070092957 Example 17, was removed by restriction digestion with BbvCI and PacI and the remaining 6.6 kb vector fragment was gel purified.
  • This vector has a chimeric gene containing the FBA promoter (SEQ ID NO:425) and CYC1 terminator bounding the coding region of the ILV5 gene of S. cerevisiae (SEQ ID NO:442). These two purified fragments were ligated overnight at 16° C. and transformed into E. coli TOP10 chemically competent cells (Invitrogen). Transformants were obtained by plating cells on LB Amp100 medium. Insertion of alsS into the vector was confirmed by restriction digestion pattern and PCR (primers N98SeqF1 and N99SeqR2, SEQ ID NOs:412 and 413).
  • a pdc1::FBAp-alsS-LEU2 disruption cassette was created by joining the FBAp-alsS segment from pRS426-FBAp-alsS to the LEU2 gene from pRS425 (ATCC No. 77106) by SOE PCR (as described by Horton et al. (1989) Gene 77:61-68) using as template pRS426-FBAp-alsS and pRS425 plasmid DNAs, with Phusion DNA polymerase (New England Biolabs Inc., Beverly, Mass.; catalog no.
  • F-540S and primers 112590-48A and 112590-30B through D, given as SEQ ID NOs:414, SEQ ID NOs:415, 416, and 417.
  • the outer primers for the SOE PCR (112590-48A and 112590-30D) contained 5′ and 3′ 50 by regions homologous to regions upstream and downstream of the PDC1 promoter and terminator.
  • the completed cassette PCR fragment was transformed into BY4741 (ATCC No. 201388) and transformants were maintained on synthetic complete media lacking leucine and supplemented with 2% glucose at 30° C. using standard genetic techniques ( Methods in Yeast Genetics, 2005, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., pp. 201-202).
  • Transformants were screened by PCR using primers 112590-30E and 112590-30F, given as SEQ ID NOs:419 and 418, to verify integration at the PDC1 locus with deletion of the PDC1 coding region.
  • the correct transformants have the genotype: BY4741 pdc1::FBAp-alsS-LEU2.
  • the expression vector containing this ilvD, pRS423 FBA ilvD (strep) prepared in Example 6 was co-transformed with vector pLH532 into yeast strain BY4741 pdc1::FBAp-alsS-LEU2. Competent cell preparation, transformation, and growth medium for selection of the transformants were the same as described in Example 6. Selected colonies were grown under oxygen-limiting conditions in 15 ml of medium in 20 ml serum bottles with stoppers. The bottles were incubated at 30° C. in a shaker with a constant speed of 225 rotations per minute.

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EP2821484A1 (en) 2015-01-07
CN102186973A (zh) 2011-09-14
NZ591244A (en) 2013-03-28
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US20140051137A1 (en) 2014-02-20
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US8951937B2 (en) 2015-02-10
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US20140030776A1 (en) 2014-01-30
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EP2821484B1 (en) 2016-06-29

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