EP1070120A1

EP1070120A1 - Amp deaminase

Info

Publication number: EP1070120A1
Application number: EP99919138A
Authority: EP
Inventors: Jens Lerchl; Andreas Reindl
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1998-04-01
Filing date: 1999-03-25
Publication date: 2001-01-24
Also published as: AU3702199A; JP2002527039A; CA2325054A1; WO1999050400A1

Abstract

The invention relates to a DNA which codes for a polypeptide with AMP deaminase (EC 3.5.4.6, adenosine triphosphate aminohydrolase) activity. The invention also relates to the use of this nucleic acid for producing a test system.

Description

AMP deaminase

description

The present invention relates to a DNA coding for a polypeptide with AMP deaminase (EC 3.5.4.6, adenosine triphosphate aminohydrolase) activity. In addition, the invention relates to the use of a nucleic acid coding for a protein with AMP deaminase activity of plant origin for the production of a test system for the identification of inhibitors of AMP deaminase. The invention further relates to the use of the nucleic acid coding for plant AMP deaminase for the production of plants with increased resistance to inhibitors of AMP deaminase.

Plants are able to synthesize their cell components from carbon dioxide, water and inorganic salts.

This process is only possible by using biochemical reactions to build up organic substances. Plants must also synthesize the nucleotides as components of the nucleic acids de novo.

It can be assumed that the efficient formation, use and distribution of the nucleotides strongly influence the cell division and the growth of a plant. Since plants rely on a functioning nucleotide metabolism, this metabolism is a possible target for the use of herbicides. Some known active substances (eg 5'-phosphohydantocidin, alanosine or hadacidin) inhibit adenylosuccinate synthase (Stayton et al., 1983, Curr. Top. Cell. Regul., 22, 103-141; Siehl et al., 1996, Plant Physiol., 110, 753-758). The reaction catalyzed by the adenylosuccinate synthetase is shown in Figure 1. Hydantocidin acts as a prodrug. The active ingredient is metabolized in planta by phosphorylation on the 5'OH group to give the herbicide (Siehl et al., 1996, Plant Physiol., 110, 753-758).

In addition to the enzyme reactions of de novo purine biosynthesis (eg adenylosuccinate synthetase), recycling processes and degradation mechanisms are an important principle for regulating nucleotide metabolism. However, the AMP deaminase occupies a special position. AMP (adenosine monophosphate) can also be deaminated back to IMP (inosine 5 'phosphate). The enzyme catalyzes the following reaction: 2

AMP + H ₂ 0 <-> IMP + NH ₄

The protein was partially purified from various plants and regulatory properties were examined, e.g. from spinach leaves (Yoshino and Murakami, 198, Z. Plant Physiology, 99, pp. 331-338), Jerusalem artichokes (Jerusalem Artichokes (Le Floc'h and La fleuriel, 1983, Physiologie Vergetale, 21 (1), 15- 2), pea seeds (Turner and Turner, 1961, Biochem. J. 79, 143) and cell cultures of Catharantus roseus, small evergreen (Yabuki et al. 1992, Phytochemistry, 31 (6), 1905-1909). The enzyme appears to play a central role in the regulation of the adenylate pool of a cell (Chapman and Atkinson, 1973, J. Biol. Former, 248, 8309; Solano and Coffee, 1978; Yoshino et al., 1979).

It could be shown that the known natural product coformycin shows herbicidal activity on plants and that the active substance in its phosphorylated form (5'-phosphocoformycin) is the actual inhibitor of AMP deaminase (Frieden et al., 1980, Biochem. 5303; Merkler et al., 1990, Biochem. 29, 8358-8364; Dancer et al., 1997, Plant Physiol., 114 (1), 119-129). The patent specification WO 96/01326 describes a method for the search for herbicides in an AMP deaminase enzyme test (see also: Pillmoor Plastic. Sci., 1998, 52, 75-80).

Genes encoding AMP deaminases have been isolated from many organisms. Gene families of AMP deaminase appear to be present in mammals (Morisaki et al. 1990, J. Biol. Chem. 265 (20), 11482-11486). Further coding sequences were isolated from Schizosaccharomyces pombe (accession P50998) and Saccharomyces cerevisiae (accession P15274). Only adenine deaminases are known from bacteria; AMP deaminases could not be isolated. By means of sequence comparisons, so-called est sequences from rice (GenBank Acc: C26026) and Arabidopsis (T21250) with similarity to yeast AMP deaminases can be found. Complete cDNA sequences of plant AMP deaminases have not yet been described.

The object of the present invention was to isolate a complete plant cDNA coding for the enzyme AMP deaminase and its functional expression in bacterial or eukaryotic cells for the simple and inexpensive extraction of the enzyme for the implementation of inhibitor-enzyme binding studies.

Another object of the invention was the overexpression of the AMP-Deaminase gene in plants for the production of plants which are tolerant of inhibitors of AMP-Deaminase. 3

The object was achieved by isolating the gene coding for the enzyme AMP deaminase vegetable ^{^,} and its functional expression in bacterial or plant cells or plants.

A first object of the present invention is a DNA sequence SEQ ID NO: 1 containing the coding region of a plant AMP deaminase from Arabidopsis thaliana (see Figure 2).

The invention further relates to DNA sequences which are derived from or hybridize with this SEQ ID NO: 1 and which code for a protein which has the biological activity of an AMP deaminase.

The invention also relates to expression cassettes, the sequence of which encode an Arabidopsis thaliana AMP deaminase or its functional equivalent. The nucleic acid sequence can e.g. be a DNA or a cDNA sequence.

The expression cassettes according to the invention also contain regulatory nucleic acid sequences which control the expression of the coding sequence in the host cell. According to a preferred embodiment, an expression cassette according to the invention comprises upstream, i.e. at the 5 'end of the coding sequence, a promoter and downstream, i.e. at the 3 'end, a polyadenylation signal and, if appropriate, further regulatory elements which are operatively linked to the intermediate coding sequence for the AMP deaminase gene. An operative link is understood to mean the sequential arrangement of promoter, coding sequence, terminator and, if appropriate, further regulatory elements in such a way that each of the regulatory elements can fulfill its function as intended when expressing the coding sequence.

An expression cassette according to the invention is produced by fusing a suitable promoter with a suitable AMP deaminase DNA sequence and a polyadenylation signal according to common recombination and cloning techniques, as described, for example, in T. Maniatis, EF Fritsch and J. Sambrook, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY (1989) and in TJ Silhavy, ML Berman and LW Enquist, Experiments with Gene Fusions, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY (1984) and in Ausubel, FM et al., Current Protocols in Molecular Biology, Greene Publishing Assoc. and Wiley-Interscience (1987). 4

Sequences are particularly preferred which ensure targeting in the apoplasts, in plastids, the vacuole, the mitochondrium, the endoplasmic reticulum (ER) or, due to the lack of corresponding operative sequences, a retention in the compartment of formation, the cytosol ( Kermode, Crit. Rev. Plant Sςi. 15, 4 (1996), 285-423).

As an example, the plant expression cassette can be installed in the tobacco transformation vector pBinAR-Hyg (see example 5).

In principle, any promoter which can control the expression of foreign genes in plants is suitable as promoters of the expression cassette according to the invention. In particular, a plant promoter or a plant virus-derived promoter is preferably used. The CaMV 35S promoter from the cauliflower mosaic virus (Franck et al., Cell 21 (1980) 285-294) is particularly preferred. This promoter contains different recognition sequences for transcriptional effectors, which in their entirety lead to permanent and constitutive expression of the introduced gene (Benfey et al., EMBO J. 8 (1989) 2195-2202).

The expression cassette according to the invention can also contain a chemically inducible promoter, by means of which the expression of the exogenous AMP deaminase gene in the plant can be controlled at a specific point in time. Such promoters as e.g. the PRPl promoter (Ward et al., Plant. Mol. Biol. 22 (1993), 361-366), a promoter inducible by salicylic acid (WO 95/1919443), one inducible by benzenesufonamide

(EP 388186), one that can be induced by tetracycline (Gatz et al., (1992) Plant J. 2,397-404), one that can be induced by abscisic acid (EP335528) or one that can be induced by ethanol or cyclohexanone (W09321334) Promoters are described in the literature and can include be used.

Furthermore, promoters are particularly preferred which ensure expression in tissues or parts of plants in which the biosynthesis of purines or their precursors takes place. Promoters that ensure leaf-specific expression should be mentioned in particular. The promoter of the cytosolic FBPase from potatoes or the ST-LSI promoter from potatoes should be mentioned (Stockhaus et al., EMBO J. 8 (1989) 2445-245).

With the help of a seed-specific promoter, a foreign protein can be stably expressed in the seeds of transgenic tobacco plants up to a proportion of 0.67% of the total soluble seed protein. 5 den (Fiedler and Conrad, Bio / Technology 10 (1995), 1090-1094). The expression cassette according to the invention can therefore contain, for example, a seed-specific promoter (preferably the phaseolin promoter, the USP or LEB4 promoter), the LEB4 signal peptide, the gene to be expressed and an ER retention signal.

Many legumes transport fixed nitrogen in the form of ureids from the nodules into the above-ground tissues (Schubert, 1986, Ann. Rev. Plant Phys. 37, 539-574). Ureides are formed through purine biosynthesis. With the help of a node (nodule) specific promoter, the AMP deaminase expression and thus the ureide biosynthesis can be modified in legumes. Accordingly, gene expression cassettes according to the invention can contain the promoter of the phosphoribosyl pyrophosphate amidotransferase from Glycine max (see also Genbank Accession number U87999) or another node-specific promoter as described in EP 249676.

The inserted nucleotide sequence coding for an AMP deaminase can be produced synthetically or obtained naturally or contain a mixture of synthetic and natural DNA components. In general, synthetic nucleotide sequences with codons are generated which are preferred by plants. These codons preferred by plants can be determined from codons with the highest protein frequency, which are expressed in most interesting plant species. When preparing an expression cassette, various DNA fragments can be manipulated in order to obtain a nucleotide sequence which expediently reads in the correct direction and which is equipped with a correct reading frame. To connect the DNA fragments to one another, adapters or linkers can be attached to the fragments.

The sequence homology between AMP deaminase from yeast and from plant is 57% at the DNA level in relation to a selected, highly homologous sub-region, for example in the region of base 1345-2715 of sequence M30449 (Genbank Accession Number), created using the BLAST program ( Altschul et al., (1990), J. Mol. Biol.: 215: 403-419; Gish and States, (1993), Nature Genet. §: 266-272). In the partial fragment described, regions of 20-30 nucleotides are so homologous that there is a sufficient probability of success for an oligonucleotide-based screening for AMP deaminase from other plants. Methods of hybridization with short oligonucleotides for the detection of DNA sequences to be detected, which only have good homology to the comparison sequence in small areas, are described in Sambrook et al. 6

(1989, Cold Spring Harbor Laboratory Press: ISBN 0-87969-309-6).

The invention also relates to functionally equivalent DNA sequences which code for an AMP deaminase gene and which, based on the total length of the gene, have a sequence homology with the DNA sequence SEQ ID NO: 1 of 40 to 100%.

Preferred objects of the invention are functionally equivalent DNA sequences which code for an AMP deaminase gene and which, based on the total length of the gene, have a sequence homology with the DNA sequence SEQ ID NO: 1 of 60 to 100%.

A particularly preferred object of the invention are functionally equivalent DNA sequences which code for an AMP deaminase gene and which, based on the total length of the gene, have a sequence homology with the DNA sequence SEQ ID NO: 1 of 80 to 100%.

Sequences which are functionally equivalent and which code for an AMP deaminase gene are, according to the invention, those sequences which, despite a different nucleotide sequence, still have the desired functions. Functional equivalents thus include naturally occurring variants of the sequences described herein as well as artificial, e.g. artificial nucleotide sequences obtained by chemical synthesis and adapted to the codon use of a plant.

A functional equivalent is understood to mean, in particular, natural or artificial mutations of an originally isolated sequence coding for an AMP deaminase, which furthermore show the desired function. Mutations include substitutions, additions, deletions, exchanges or insertions of one or more nucleotide residues. Thus, for example, the present invention also encompasses those nucleotide sequences which are obtained by modification of this nucleotide sequence. The aim of such a modification can e.g. further narrowing down the coding sequence contained therein or e.g. also be the insertion of further restriction enzyme interfaces.

Functional equivalents are also those variants whose function is weakened or enhanced compared to the original gene or gene fragment.

In addition, artificial DNA sequences are suitable as long as, as described above, they impart the desired property of increasing the IMP content in the plant by overexpressing the AMP deaminase gene in crop plants. Such artificial DNA 7 sequences can comprise or be determined by in vitro selection, for example by back-translation means Mo- lecular ^£ modeling of proteins constructed that tivity AMP deaminase activated. Coding DNA sequences which are obtained by back-translating a polypeptide sequence according to the codon usage specific for the host plant are particularly suitable. The specific codon usage can easily be determined by a person skilled in plant genetic methods by computer evaluations of other, known genes of the plant to be transformed.

Sequences which code for fusion proteins are to be mentioned as further suitable equivalent nucleic acid sequences according to the invention, a component of the fusion protein being a vegetable AMP deaminase polypeptide or a functionally equivalent part thereof. The second part of the fusion protein can e.g. be another polypeptide with enzymatic activity or an antigenic polypeptide sequence that can be used to detect AMP deaminase expression (e.g. myc-tag or his-tag). However, this is preferably a regulatory protein sequence, such as e.g. a signal or transit peptide that directs the AMP deaminase protein to the desired site of action.

The promoter and terminator regions according to the invention should expediently be provided in the transcription direction with a linker or polylinker which contains one or more restriction sites for the insertion of this sequence. As a rule, the linker has 1 to 10, usually 1 to 8, preferably 2 to 6, restriction sites. In general, the linker has a size of less than 100 bp, often less than 60 bp, but at least 5 bp within the regulatory ranges. The promoter according to the invention can be both native or homologous and foreign or heterologous to the host plant. The expression cassette according to the invention contains in the 5 '-3' transcription direction the promoter according to the invention, any sequence and a region for the transcriptional termination. Different termination areas are interchangeable.

Manipulations which provide suitable restriction sites or which remove superfluous DNA or restriction sites can also be used. Where insertions, deletions or substitutions such as transitions and transversions come into question, in vitro mutagenesis, "primer pair", restriction or ligation can be used. With suitable manipulations, such as restriction, "chewing-back" or filling in of overhangs for "bluntends", complementary ends of the fragments can be made available for the ligation. 8th

Of particular importance for the success according to the invention is that - appending the specific ER retention signal SEKDEL (Schouten, A. et al. Plant Mol. Biol. 30 (1996), 781-792), the average expression level is thus tripled or quadrupled . Other retention signals, which occur naturally in plant and animal proteins located in the ER, can also be used to construct the cassette.

Preferred polyadenylation signals are plant polyadenylation signals, preferably those which essentially correspond to T-DNA polyadenylation signals from AgroJacterium-m tumefaciens, in particular gene 3 of T-DNA (octopine synthase) of the Ti plasmid pTiACH5 (Gielen et al., EMBO J. 3 (1984) 835 ff) or functional equivalents.

To transform a host plant with a DNA coding for an AMP deaminase, an expression cassette according to the invention is inserted as an insert into a recombinant vector, the vector DNA of which contains additional functional regulatory signals, for example sequences for replication or integration. Suitable vectors are described in "Methods in Plant Molecular Biology and Biotechnology" (CRC Press), Chap. 6/7, p.71-119.

The transfer of foreign genes into the genome of a plant is called transformation. The methods described for the transformation and regeneration of plants from plant tissues or plant cells for transient or stable transformation are used. Suitable methods are the protoplast transformation by polyethylene glycol-induced DNA uptake, the biolistic approach with the gene cannon, the electroporation, the incubation of dry embryos in DNA-containing solution, the microinjection and the gene transfer mediated by Agrobacterium. The methods mentioned are described, for example, in B. Jenes et al., Techniques for Gene Transfer, in: Transgenic Plants, Vol. 1, Engineering and Utilization, published by S.D. Kung and R. Wu, Academic Press (1993) 128-143 and in Potrykus Anu.Rev.Plant Physiol.Plant Molec.Biol. 42 (1991) 205-225). The construct to be expressed is preferably cloned into a vector which is suitable for transforming AgroJbaσter u-m turne faciens, for example pBin19 (Bevan et al., Nucl. Acids Res. 12 (1984) 8711).

Agrobacteria transformed with an expression cassette according to the invention can also be used in a known manner to transform plants, in particular crop plants, such as cereals, maize, soybeans, rice, cotton, sugar beet, canola, sunflower, 9

Flax, hemp, potato, tobacco, tomato, rapeseed, alfalfa, lettuce and - the various tree, nut and wine species and legumes are used, e.g. by bathing wounded leaves or leaf pieces in an agrobacterial solution and then cultivating them in suitable media.

The biosynthesis site of purines is generally the leaf tissue, so that leaf-specific expression of the AMP deaminase gene is useful. However, it is obvious that the purine bio-synthesis need not be limited to the leaf tissue, but can also be tissue-specific in all other parts of the plant, for example in fatty seeds.

Many legumes transport fixed nitrogen in the form of ureids from the nodules into the above-ground tissues (Schuber, 1986, Ann. Rev. PlantPhys. 37,539-574). Ureides are formed using purine biosynthesis. With the aid of a node (nodule) specific promoter, the AMP deaminase expression and thus the ureide biosynthesis can be specifically identified in legumes, e.g. using the promoter of phosphoribosyl pyrophosphate amidotransferase from Glycine max (see also Genbank Accession number U87999) or using another node-specific promoter (e.g. described in EP249676).

In addition, constitutive expression of the exogenous AMP deaminase gene is advantageous. On the other hand, inducible expression may also appear desirable.

Using the recombination and cloning techniques cited above, the expression cassettes according to the invention can be cloned into suitable vectors which enable their multiplication, for example in E. coli. Suitable cloning vectors include pBR332, pUC series, M13mp series and pACYC184. Binary vectors which can replicate both in E. coli and in agrobacteria are particularly suitable.

Another object of the invention relates to the use of an expression cassette according to the invention for the transformation of plants, plant cells, plant tissues or parts of plants. The aim of the use is preferably to increase the AMP deaminase content in the plant.

Depending on the choice of the promoter, the expression can take place specifically in the leaves, in the seeds or in other parts of the plant. Such transgenic plants, their reproductive material as well 10 whose plant cells, tissues or parts are a further subject of the present invention.

The expression cassette according to the invention can also be used to transform bacteria, cyanobacteria, yeasts, filamentous fungi and algae with the aim of producing sufficient amounts of the enzyme AMP-deaminase.

Another object of the invention is a protein from Arabidopsis thaliana characterized by the amino acid sequence SEQ ID NO: 2 or derivatives or parts of this protein with AMP deaminase activity. Compared to Saccharomyces cerevisiae, the homology at the amino acid level is 43-47% identity (see Figure 4).

The invention also relates to vegetable proteins with AMP deaminase activity with an amino acid sequence homology to the Arabidopsis thaliana AMP deaminase of 20-100% identity.

Vegetable proteins with AMP deaminase activity with an amino acid sequence homology to the Arabidopsis thaliana AMP deaminase of 50-100% identity are preferred.

Vegetable proteins with AMP deaminase activity with an amino acid sequence homology to the Arabidopsis thaliana AMP deaminase of 80-100% identity are particularly preferred.

As already mentioned, AMP deaminase is a suitable target for herbicides. In order to be able to find even more efficient AMP deaminase inhibitors, it is necessary to provide suitable test systems with which inhibitor-enzyme binding studies can be carried out. For this purpose, for example, the complete cDNA sequence of the AMP deaminase from Arabidopis thaliana is cloned into an expression vector (pQE, Qiagen) and overexpressed in E. coli (see Example 3).

The AMP deaminase protein expressed with the aid of the expression cassette according to the invention is particularly suitable for the detection of inhibitors specific for AMP deaminase.

For this purpose, the AMP deaminase can be used, for example, in an enzyme test in which the activity of the AMP deaminase is determined in the presence and absence of the active substance to be tested. By comparing the two activity determinations, a qualitative and quantitative statement can be made about the inhibitory behavior of the active substance to be tested (see Example 4). 11

Using the test system according to the invention, a large number of chemical compounds can be checked quickly and easily for herbicidal properties. The method makes it possible to selectively reproducibly select those with great potency from a large number of substances, in order to subsequently carry out further in-depth tests known to the person skilled in the art.

The invention further relates to herbicides which can be identified using the test system described above.

Overexpression of the gene sequence coding for an AMP deaminase in a plant results in increased resistance to inhibitors of AMP deaminase. The transgenic plants produced in this way are also the subject of the invention.

The effectiveness of the expression of the transgenically expressed AMP-Deaminase gene can be determined, for example, in vitro by an increase in shoot meristem or by a germination test. In addition, a change in the type and level of expression of the AMP deaminase gene and its effect on the resistance to inhibitors of AMP deaminase on test plants can be tested in greenhouse experiments.

The invention also relates to transgenic plants transformed with an expression cassette according to the invention, and to transgenic cells, tissues, parts and propagation material of such plants. Transgenic crop plants, such as e.g. Barley, wheat, rye, corn, soy, rice, cotton, sugar beet, canola, sunflower, flax, hemp, potato, tobacco, tomato, rapeseed, alfalfa, lettuce and the various tree, nut and wine species, as well as legumes.

The invention further relates to plants which, after expression of the DNA SEQ ID NO: 1, have an increased IMP content in the plant.

In the context of the present invention, increasing the inosine-5 '-phosphate (IMP) content means for at least the artificially acquired ability of an increased IMP biosynthesis by functional overexpression of the AMP deaminase gene in the plant compared to the non-genetically modified plant a generation of plants. 12

The invention is illustrated by the following examples, but is not limited to these:

Examples

A. Genetic engineering processes on which the exemplary embodiments are based:

General cloning procedures

Cloning methods such as Restriction cleavages, agarose gel electrophoresis, purification of DNA fragments, transfer of nucleic acids to nitrocellulose and nylon membranes, linking of DNA fragments, transformation of Escherichia coli cells, cultivation of bacteria and sequence analysis of recombinant DNA were carried out as in Sambrook et al. (1989) (Cold Spring Harbor Laboratory Press: ISBN 0-87969-309-6).

Sequence analysis of recombinant DNA

The sequencing of recombinant DNA molecules was carried out with a laser fluorescence DNA sequencer from ABI according to the method of Sanger (Sanger et al. (1977) Proc. Natl. Acad. Sci. USA74, 5463-5467). Fragments resulting from a polymerase chain reaction were sequenced and checked in order to avoid polymerase errors in constructs to be expressed.

Analysis of total RNA from plant tissues

Total RNA from plant tissues was isolated as in Logemann et al. ((1987) Anal. Biochem. 163, 21). For the analysis, 20 μg RNA were separated in a 1.5% agarose gel containing formaldehyde and transferred to nylon membranes (Hybond, Amersham). The detection of specific transcripts was carried out as described for Amasino ((1986) Anal. Biochem. 152,

304). The cDNA fragments used as a probe were radioactively labeled with a random primed DNA labeling kit (Boehringer, Mannheim) and hybridized according to standard methods (see Hybond user instructions, Amersham). Hyridization signals were visualized by autoradiography using X-OMAT AR films from Kodak.

The bacterial strains used below (E. coli, XL-I Blue) were obtained from Stratagene or Pharmacia in the case of NP66. The Agrobacterium strain used for plant transformation (Agrobacterium tumefaciens, C58C1 with the plasmid pGV2260 or pGV3850kan) was developed by Deblaere et al. (Nucl. Acids 13

Res. 13 (1985) 4777). Alternatively, the agrobacterial strain LBA4404 (Clontech) or other suitable strains can be used. For cloning, the vectors pUC19 (Yanish-Perron, Gene 33 (1985), 103-119) pBluescript SK- (Stratagene), pGEM-T (Promega), pZerO (Invitrogen), pBinl9 (Bevan et al., Nucl. Acids Res. 12 (1984) 8711-8720) and pBinAR (Höfgen and Willmitzer, Plant Science 66 (1990) 221-230).

example 1

PCR amplification of the AMP deaminase gene using synthetic oligonucleotides.

The Arabidopsis est clone coding for the AMP deaminase was obtained from the Arabidopsis Biological Resource Center (Ohio State University). It is a partial cDNA clone (T21250) that does not correspond to the full-length transcript of the AMP deaminase. A PCR amplification of the Arabidopsis AMP deaminase partial fragment was carried out in a DNA thermal cycler from Perkin Elmer. The oligonucleotides used

5 'primers CGAGATAGCTCGTAAC and 3' PRIMER AGCCCACTCATATTATT were taken from the determined sequence. The reaction mixtures contained 8 ng / μl genomic DNA from Escherichia coli, 0.5 μM of the corresponding oligonucleotides, 200 μM nucleotides (Pharmacia), 50 mM KCl, 10 mM Tris-HCl (pH 8.3 at 25 ° C., 1.5 mM) MgCl ₂ ) and 0.02 U / μl Taq polymerase (Perkin Elmer).

The amplification conditions were set as follows:

Annealing temperature: 52 ° C, 1 min

Denaturation temperature: 92 ° C, 1 min

Elongation temperature: 72 ° C, 1.5 min

Number of cycles: 40

The resulting fragment comprises a small part of the est clone T21250, with the aid of which a heterologous screening of an Arabidopsis thaliana cDNA bank was carried out (Stratagene). 3.0 × 10 ⁵ lambda phages from the cDNA library from Arabidopsis thaliana (Stratagene) were plated on agar plates with E. coli XLI-Blue as a bacterial strain. The phage DNA was analyzed using

Standard methods (Sambrook et al. (1989); Cold Spring Harbor Laboratory Press: ISBN 0 = 87969-309-6) transferred to nitrocellulose filters (Gelman Sciences) and fixed on the filters. The PCR fragment described above served as hybridization probes, which were radioactively labeled with the aid of a “Multiprime DNA labeling System” (Amersham Buchler) in the presence of α- ³² P-dCTP (specific activity 3000 Ci / mmol) according to the manufacturer's instructions. 14

The membranes were hybridized after prehybridization ~ at 60 ° C in 3 x SSPE, 0.1% sodium dodecyl sulfate (w / v), 0.02% polyvinylpyrolidone (w / v), 0.02% Ficoll 400 (w / v) and 50 mg / ml calf thymus DNA for 12-16 hours (Sambrook et al. (1989); Cold Spring Harbor Laboratory Press: ISBN 0-87969-309-6). The filters were then washed in 2 x SSPE, 0.1% sodium dodecyl sulfate (w / v) at 60 ° C. for 60 minutes. Positive hybridizing phages were visualized by autoradiography and purified and isolated using standard techniques.

Example 2

Sequence analysis of the cDNA clones coding for a protein with AMP deaminase activity.

This resulted in 64 cDNA clones coding for a polypeptide with high homologies to AMP deaminase from yeast (see Figure 4). The two longest clones are identical and show a 2880 base pair long EcoRI fragment in the restriction digest. This longest clone coding for the AMP deaminase from Arabidopsis thaliana was called AMPl. The plasmid is called pBS-AMPl. The cDNA (see Figure 2) has an open reading frame of 2578 base pairs with a stop codon in position 2579-2581. The amino acid sequence begins with the third base after the linker sequences (bold ends of the sequence in Figure 2) in the third reading frame and can be translated into an 860 amino acid polypeptide, or from the first methionine start codon into a polypeptide of 839 amino acids (see Figure 3). Alternatively, the methionine in position 46 can be used, so that a polypeptide of 824 amino acids would result.

While protein activity is cytosolically localized in yeast, cytosolic and potentially mitochondrial activity has been described in plants (Yoshino and Murakami, 198, Z. Plant Physiology, 99, pp. 331-338). Based on the reading frame of the present cDNA sequence, it can be deduced that it could possibly be the mitochondrial form or the cytosolic form, which can optionally arise through the use of different start codons. It is striking that at the beginning of the reading frame from base 3 of the coding sequence, a large number of hydrophilic serine and threonine residues are present alternately with aliphatic amino acid residues in front of the methionine codons, which indicates a transit sequence for mitochondria or plastids. It is generally assumed that purine biosynthesis takes place in the plastid. However, it has recently been shown that the enzymes of purine biosynthesis are also localized in mitochondria (Atkins et al. 1997, Plant Physiol. 113, 127-135). Because of the 15 serasters of the present cDNA sequence suggests that it could possibly be the mitochondrial, plasmid or cytosolic form, which can be created by using different start codons. The two longest clones show a continuous open reading frame with two potential start codons at the N-terminus. Compared to the yeast sequence, the second start codon is approximately at the position where the yeast sequence also begins (see Figure 4). Over the entire protein length, the plant sequence is approximately 59-63% similar to the yeast sequence and approximately 43-47% identical depending on the choice of the comparison parameters

(Lasergene software, MegAlign program). It is striking that the N-terminus of the plant AMP deaminase has only weak homology in contrast to the C-terminus of the yeast sequence.

Example 3

Generation of overexpression vectors in E. coli

The following oligonucleotide sequences were derived from the determined sequence and provided with a BamHI restriction site and two overhanging bases. The oligonucleotides are underlined and numbered in Figure 2. Potential methionine start codons are shown in bold.

1.5 'primer aaggatccATGTTACTCTCTCTTCTGAG,

2.5 'primer aaggatccATGGAACCCAATATTTAC,

3.5 'primer aaggatccATGCATTTCAAGGCAC,

4. 3 'primer aaggatccTTATGGAACAACTTCATCAG,

The use of the three different 5 'primers in combination with the 3' primer leads to PCR products of different lengths (fragment I, II, III) which follow the complete reading frame (fragment I, primer 1 + 4) correspond to the first Met start codon (fragment II, primer 2 +4) or the second start codon (fragment III, 3 + 4).

The PCR reaction mixtures contained 8 ng / μl pBS-AMPl DNA, 0.5 μM of the corresponding oligonucleotides, 200 μM nucleotides (Pharmacia), 50 mM KCl, 10 mM Tris-HCl (pH 8.3 at 25 ° C., 1, 5 mM MgCl ₂ ) and 0.02 U / μl Taq polymerase (Perkin Elmer). The amplification conditions were set as follows:

Annealing temperature: 52 ° C, 1 min

Denaturation temperature: 92 ° C, 1 min Elongation temperature: 72 ° C, 2.5 min 16

Number of cycles: 30

The PCR fragments were cloned into the overexpression vectors pET15b, pETlla and pQE9 and used for protein production by means of IPTG-5 induction according to standard methods (see manual: The Quiaexpressionist (1992), Quuiagen, Hilden).

Example 4

10 Enzyme assay of the vegetable AMP deaminase from E. coli using overexpression cultures

E.coli was subjected to pressure digestion on the French Press under maximum pressure in a 20 ml pressure chamber or using a

15 glass ball mill (IMA disintegrator) unlocked. 10 ml buffer (0.1M KH ₂ P0 ₄ ; pH 7.5; 0.4M sucrose, 0.1 mM DTT) are used per 1 g cell pellet. By adding 2.5 times the amount of glass beads (d = 0.5 mm), the pellet in the glass ball mill is disrupted for 20 min at 4 ° C. and 2500 rpm. The digestion is at 4 ° C and

20 centrifuged 100,000g for 20 minutes. The enzyme activity was determined in a photometric assay by measurement at 260 nm on a photometer (Uvikon 933, Kontron). The choice of overexpression vectors also made it possible to purify the AMP deaminase using the standard histidine anchor.

25 standard methods in one step towards homogeneity if DTT was omitted in the digestion buffer (cf. also manual: The Quiaexpressionist, Quiagen, Hilden).

The homogenate was buffered in the following medium by dialysis in 40 mM 30 citrate, pH 6.5 (adjusted with 5 N NaOH), 0.05% BSA (w / v), 100 mM KCl.

Each 10-100μl of the rebuffered enzyme fraction was made up to 700 μl with buffer and by adding 100 μl of a 1 mM AMP solution

35 solution, 0.5 mM ATP solution and 1 μM diadenosine pentaphosphate solution measured the decrease in extinction over 2-10 min against a reference cuvette with 700 μl reaction buffer and 100 μl of a protein homogenate of untransformed E. coli culture. Equal amounts of total protein were used for the measurements of the reference against the measured value

40 used.

Example 5

Generation of plant expression cassettes 45 17

In the plasmid pBinl9 (Bevan et al. (1980) Nucl. Acids Res. 12, ~ 8711), a 35S CaMV promoter as an EcoRI-Kpnl fragment (corresponding to nucleotides 6909-7437 of the Cauliflower mosaic virus (Franck et al (1980) Cell 21, 285)). The polyadenylation signal of gene 3 of the T-DNA of the Ti plasmid pTiACH5 (Gielen et al., (1984) EMBO J. 3, 835), nucleotides 11749-11939 was isolated as a PvuII-HindiII fragment and after addition of Sphl -Line cloned to the PvuII interface between the SpHI-HindIII interface of the vector. The plasmid pBinAR was produced (Höfgen and Willmitzer (1990) Plant Science 66, 221-230). The PCR fragments I, II and III (see above) were cloned into the BamHI site of the vector pBinAR in both orientations and used to transform tobacco plants.

The resulting plasmids have the names pBinAMP-20, pBinαAMP-0, pBinAMP-0, pBinαAMP-0, pBinAMP + 26, pBintxAMP + 26 and correspond to fragments I, II, III described in Example 3 from the PCR batches described above.

Example 6

Production of transgenic tobacco plants

The plasmids pBinAMP-20, pBinαAMP-20, pBinAMP-0, pBinαAMP-0, pBinAMP + 26, pBinαAMP + 26 were found in Agrobacterium tumefaciens

C58Cl: pGV2260 transformed (Deblaere et al, 1984, Nucl. Acids. Res. 13, 4777-4788). To transform tobacco plants (Nicotiana tabacum cv. Samsun NN), a 1:50 dilution of an overnight culture of a positively transformed agrobacterial colony in Murashige-Skoog medium ((1962) Physiol. Plant. 15, 473) with 2% sucrose ( 2MS medium) is used. Leaf disks of sterile plants (each about 1 cm ² ) were incubated in a Petri dish with a 1:50 agrobacterial dilution for 5-10 minutes. This was followed by a 2-day incubation in the dark at 25 ° C. on 2MS medium with 0.8% Bacto agar. The cultivation was continued after 2 days with 16 hours of light / 8 hours of darkness and in a weekly rhythm on MS medium with 500 mg / 1 claforan (cefotaxime sodium), 50 mg / 1 kanamycin, 1 mg / 1 benzylaminopurine (BAP ), 0.2 mg / 1 naphthylacetic acid and 1.6 g / 1 glucose continued. Growing shoots were transferred to MS medium with 2% sucrose, 250 mg / 1 Claforan and 0.8% Bacto agar.

Regenerated shoots are obtained on 2MS medium with kanamycin and claforan, transferred to soil after rooting and after cultivation for two weeks in a climatic chamber in a 16 hour light / 8 hour dark rhythm at 60% humidity for foreign gene expression or altered metabolite contents and phenotypic 18th

Growth characteristics examined. Modified nucleotide contents can ^*, for example, according to the method of Stitt et al. (1982, FEBS Letters, 145, 217-222).

Example 7

To demonstrate the tolerance of the AMP deaminase overexpressing transgenic tobacco plants to AMP deaminase inhibitors, these were treated with different amounts of coformycin or other AMP deaminase inhibitors. In all cases it could be shown in the greenhouse that the plants overexpressing an AMP deaminase show a tolerance towards the inhibitors used in comparison to the control.

Claims

19 patent claims

1. DNA sequence containing the coding region of a plant 5 AMP deaminase, characterized in that this DNA sequence has the nucleotide sequence SEQ ID No: 1.

2. DNA sequences which with the DNA sequence SEQ ID NO: 1 according to claim 1 or parts thereof or derivatives which by insert

10 tion, deletion or substitution are derived from these sequences, hybridize and code for a protein which has the biological activity of an AMP deaminase.

3. Expression cassette containing regulatory nucleic acid sequences and a DNA sequence according to claim 1 or 2.

4. Protein with AMP deaminase activity, containing an amino acid sequence which is a partial sequence of at least 100 amino acids from SEQ ID NO: 2.

20th

5. Protein according to claim 4, characterized in that it contains the partial sequence 50-750 from SEQ ID NO: 2 as the amino acid sequence.

6. Protein according to claim 5, characterized in that it contains the sequence shown in SEQ ID NO: 2 as the amino acid sequence.

7. Bacteria containing a DNA sequence according to claim 1 or 30 2 or parts thereof or derivatives which are derived from these sequences by insertion, deletion or substitution.

8. yeasts containing a DNA sequence according to claim 1 or 2 or parts thereof or derivatives which by insertion, dele-

35 tion or substitution are derived from these sequences.

9. plant cells containing an expression cassette according to claim 3.

40 10. Plants containing an expression cassette according to claim 3.

45 fig. 20th

11. Use of DNA sequences according to claim 1 or 2 or ^s parts or derivatives which are derived from these sequences by insertion, deletion or substitution, for introduction into pro- or eukaryotic cells, these sequences optionally with control elements, which ensure transcription and translation in the cells, are linked and lead to the expression of a translatable mRNA which brings about the synthesis of an AMP deaminase.

10 12. Use of the expression cassette according to claim 3 for the transformation of plants.

13. Use of the expression cassette according to claim 3 for the production of a test system for the identification of inhibitor

15 of the AMP deaminase.

14. Use of a plant containing an expression cassette according to claim 3 for the production of AMP deaminase.

15. Use of the expression cassette according to claim 3 for the production of plants with increased resistance to inhibitors of AMP deaminase by increased expression of a DNA sequence according to claim 1 or 2.

25 16. Use of the expression cassette according to claim 3 for the production of plants with an increased content of IMP.

17. Test system based on the expression of an expression cassette according to claim 3 for the identification of inhibitors

30 of the AMP deaminase.

18. Herbicidal active ingredients, identifiable by means of a test system according to claim 17.

35 19. A method for transforming a plant, characterized in that an expression cassette according to claim 3 is introduced into a plant cell, into callus tissue, an entire plant or protoplasts of plant cells.

40 20. Process for the production of plants with increased resistance to inhibitors of AMP deaminase by increased expression of a DNA sequence according to claim 1 or 2.

21. A method for producing plants with an increased content of 45 IMP by increased expression of a DNA sequence according to claim 1 or 2. 21

22. Plant with increased resistance to inhibitors of AMP- ^ deaminase containing an expression cassette according to claim 3.

23. Plant with an increased content of IMP containing an expression cassette according to claim 3.