CA1339012C - Dna-molecules coding for fmdh (formate dehydrogenase) control regions and structured gene for a protein having fmdh-activity and their uses - Google Patents

Abstract

The invention relates to DNA-molecules comprising DNA-sequences encoding control regions and the structural gene for a protein having formate dehydrogenase (FMDH) activity. The DNA-molecules may be combined with DNA-sequences encoding foreign genes so as to bring these genes under the stringent control of the regulation of the FMDH
regulatory sequences and/or may be combined to DNA-sequences coding for secretory signals. The invention further relates to recombinant vectors containing these DNA-molecules and micro-organisms containing the vectors or DNA-molecules.
Furthermore, the invention relates to a process for producing a useful substance by producing this substance by culturing the micro-organisms and recovering the substance.

Description

During the last decade, several yeast strains were isolated which are able to utilize methanol as an only carbon and energy source. Until recently the studies were limited to the enzymatic level and concerned mainly two species, namely Hansenula polymorpha and Candida boidinii.

The enzymatic studies revealed that in methylotrophic yeasts methanol is oxidised via formaldehyde and formate to COz by methanol oxidase (MOX), formaldehyde dehydrogenase (FMD) and formate dehydrogenase (FMDH), respectively. H202 which is generated during the first oxidation step is degraded by catalase. C1 compound is assimilated by transketalase reaction of xylulose-5-(P) and formaldehyde, the latter being derived from the dissimilatory pathway. The reaction is catalysed by dihydroxyacetone synthase (DHAS).

Growth of methylotrophic yeast on methanol is accompanied by changes in total protein composition. There are 3 major and about 5 minor proteins newly synthesized.
Further, the growth on methanol is accompanied by appearance of huge peroxisomes. These organelles bear some of the key enzymes involved in methanol metabolism, namely, MOX, DHAS and catalase (1). The other two methanol enzymes FMD and FMDH, are cytoplasmic proteins.
In methanol grown cells, the enzymes FMDH, MOX, and DHAS
constitute up to 40% of total cell protein. The methanol utilisation pathway is highly compartmentalised and the integration of these reactions is very complex.

The methanol dissimilatory enzymes are regulated by glucose catabolite repression/derepression mechanism (2).
Methanol has an additional inductive effect increasing the expression level by the factor of 2-3. In H.
PolYmor~ha, assimilatory DHAS enzyme follows this general regulation scheme, however, during growth on limiting amounts of glucose, derepression, an additional post transcriptional mech~n;sm, plays a role in the regulation.

Recently, 3 genes encoding peroxisomal enzymes were cloned from H. polymorpha and Pichia ~astoris and the analysis of nucleotide sequences of MOX genes from H.
polYmorpha (3) and P. pastoris (4) and DAS gene, which encodes DHAS from H. polymor~ha (5) revealed that a cleavable signal sequence is not required for the transport of MOX and DHAS into the peroxisome.

The promoters of some methanol genes are very efficient and their way of regulation is favourable to the industrial application. The expression of foreign proteins can be enhanced and placed under stringent control. The large amounts of proteins (MOX, DHAS) thus produced by methylotrophic yeast are stored in the peroxisomes. The understanding of this m~h~n;sm will help to solve some problems of the stability of foreign proteins in yeast.

In the field of industrial biotechnology, there is a need for microbiological regulation systems by which large amounts of a particularly desired protein can be produced under stringent control. Although there are already promoter/terminator systems available which can be used in genetic engineering systems for controlling the amount of proteins to be produced, there is still a strong need for further regulatory systems to be available since it has turned out that, in biological systems, it is advantageous to provide more systems so that the most effective one can be chosen. The present systems are far from being efficient, especially when stringent regulation and high mitotic stability is required.

It was, therefore, an object of the present invention to provide a more effective and a very easily controllable regulatory system.

The advantage of the present invention is given by providing a DNA-molecule which comprises DNA-sequences encoding control regions and the structural gene for a protein having formate dehydrogenase (FMDH) activity.

To start more comprehensive studies on basic research and biotechnological aspects of methanol utilisation, the gene encoding the cytoplasmic methanol key enzyme FMDH
was cloned. The sequence of this 1020 bp long gene and its regulatory regions have been cloned. FMDH is regulated at transcriptional level by glucose catabolite repression/derepression/methanol induction mPch~n;sm.

The DNA-molecule according to this invention is extremely useful in the biotechnology industry because of the above discussed characteristic that the expression of foreign proteins can be enhanced and placed under stringent control.

DNA-molecules having sequences which code for wild type FMDH protein may be modified by recombinant DNA
technology t~chn;ques as known in the art, so as to encode a protein showing improved biotechnological features. The recombinant DNA technology technique modifications may be carried out at the sequences coding for the structural gene and also the promoter of the control region. Hence, features with a view to a very important, over production of useful proteins and the stringent control are thus obtained.

Examples for the use of the FMDH regulatory sequences of the present invention are combinations of said DNA

1 339'J~ 2 sequences with foreign genes encoding hepatitis B virus S1-S2-S antigen and hepatitis B virus S antigen~-amylase from S. castellii and glucoamylase from S. castellii or invertase from Saccharomyces cerevisiae.

The DNA-molecules of this invention may further be combined to DNA-sequences which are coding for secretory signal, such as Hansenula polymorpha membrane translocation signals, preferably those from peroxisomal proteins, methanol oxidase and dihydroxyacetone synthase, Schawanniomces castelli~-amylase and glucoamylase signals, or Saccharomyces cerevisiae ~-factor and invertase signals.

Preparation of the DNA-molecules coding for control regions and the structural gene for protein having FMDH
activity may be obtained from natural DNA and/or cDNA
and/or chemically synthesized DNA.

Recombinant vectors can be prepared which contain the DNA
sequences according to this invention either as such, coding for the regulatory regions and/or structural genes for FMDH protein and may be combined to further DNA
sequences as discussed above. Recombinant vectors for the purposes of transferring DNA sequences into an expression system are commonly used in the art and may be properly chosen. For example, the ~ Charon 4A phage may carry the described DNA-molecules.

As micro-organisms which are suitable for the expression of the desired genes also may be selected from known micro-organisms in the art which are adapted for recombinant DNA technologies. Micro-organisms, however, who are able to tolerate high concentrations of foreign proteins are preferred.

~ 33901 2 -Most preferred are micro-organisms of the genera Candida, Hansenula or Pichia.

The mentioned micro-organisms are able to produce the desired substances either by integration of the DNA-molecules of this invention into the chromosom of the micro-organism or by maintaining the DNA-molecules on an extra chromosomal DNA-molecule via episomal vectors.

The proteins coded by foreign genes combined to the DNA-molecules of the present invention and being produced by the transformed micro-organisms can be obtained by culturing said micro-organisms in a manner known in the art and recovering the proteins as is also standard knowledge in the art.

In one aspect, the present invention provides a DNA
fragment characterized in that it comprises a promoter region of a gene coding for a protein derived from a methylotrophic yeast and having formate dehydrogenase (FMDH) activity, said gene being identical or equivalent to a FMDH gene being obtA;nAhle from the Hansenula polymorpha genome, wherein the FMDH gene is located on a 3.5 kb BamHI.HindIII fragment, said promoter region being derepressible when said methylotorophic yeast is grown on glycerol as an only carbon source and is inducible by addition of methanol.

_ - 6 The invention is now presented, in a more detailed manner, by the following specification and figures. The figures show:

Figure 1: Analysis of protei crude extracts and in vitro translation products by SDS-polyacrylamid gel electrophoresis.

Lanes 7-9 Coomassie Blue stained gel;
protein crude extracts from induced, derepressed and uninduced cells, respectively. Lane 10, purified FMDH.
Lanes 1-3 35S-labelled in vitro translation products of mRNA isolated from induced, uninduced cells and fractionated mRNA
enriched in FMDH mRNA species, respectively. Lane 4, immunoprecipitation of translation products from lane 1. Lane 5, translation of hybrid-selected mRNA.
Lane 6, immunoprecipitation of translation products from lane 5.

Figure 2: Restriction map of DNA fragment encompassing the FMDH gene.

The arrow shows the direction of transcription.

Figure 3: S1-mapping;

Lanes M1, 1, 2, 3, 4, M2, a, b, c, d, separation on alkaline agarose gel. Lanes 5, M3-separation on 6% polyacrylamide gel/8M urea. Lanes M1-M3-MW markers.
Lanes 1, 2-total protection (1) of 4.1 kb -Eco-RI/Hind III fragment (2) encompassing the gene. Lanes 3, 4-protection of 3'-end labelled 1.4 kb Bam HI/Hind III fragment;
3-protected band; 4-1.4 kb intact band.
Lane 5-protection of 1 kb Bam HI/Pst I
fragment with a single label at Bam HI
site. Lanes a, b, c, d-protection of 3'-end labelled DNA fragment containing part of the gene by mRNA preparation isolated from: induced, derepressed (1% glicerol), stationary phase of 3% glucose and mid-log phase of 3% glucose cultures, respectively.

Figure 4: Sequencing strategy - schematic representation.

DNA fragments cont~;n;ng the gene were subjected to Bal31 digestion and the resulting fragments subcloned into M13 and/or pUC type vectors. The fragments were sequenced by Sanger and in the case of doubts Maxam-Gilbert methods.

Figure Sa: Nucleotide sequence of FMDH gene and its S', 3' control regions.

Figure Sb: Nucleotide sequence of FMDH gene and its 5', 3' control regions.

Figure 5c: Nucleotide sequence of FMDH gene and its 5', 3' control regions.

Figure 6: Plasmid containing the fusion of bacterial ~-lactamase gene with FMDH promoter.

-Figure 7: Plasmid containing the hepatitis S-gene;
HARS - H. polymorpha autonomous replicating sequence; URA3 - S. cerevisiae gene; FMDH-promoter (-9 type promoter).

Figure 8: Western blot-stained by peroxidase/protein A method. Polyclonal antibodies (not clarified) were used in this experiment:

Lane a : LR9 growth on methanol Lane i : transformant w/o S-gene Lanes k, 1, m, : transformants with S-gene grown on glucose (repression) Lanes b, c, d, e, f, g: different transformants with S-gene grown on methanol Lanes n, o : 500.450 ng purified HSBAg, respectively Figures 9: Plasmid expressing ~-amylase gene;
symbols are the same in Fig 7.

Figure 10. Growth of transformants on medium containing methanol (induction). Enzyme activity (U/ml) were measured in medium and in cells (intra-cellular enzyme Level). The latter value was expressed as corresponding to 1 ml of medium.

Figure 11: The formation of halo after applying of , g the plate 50 ul of the medium from transformants (upper row) and from control untransformed strain LR9 (Lower row).

Detailed Description of the Preferred Embodiments The sequence depicted in Figure S is a preferred embodiment of the DNA - molecule according to the present invention.

- 1 33~0 1 2 Strains media vectors:

Thermophilic, homothallic strain of H. Polymorpha (ATCC
34438) was used. Yeast was grown at 37C on minimal YNB
medium as described (3, 5). Induction of methanol utilisation system was achieved by growth in minimal medium containing 1% methanol; growth on 3% glucose minimal medium resulted in repression of the system.

E. coli L90; C600recA, hsdM, araB, was used for transformation;

E. coli JM103, thi, strA, supE, endA, sbcB, hsdR, F'traD36, proAB, lacI, ZM15, and E. coli KH802 gal, met, supE, were used as host for phage M13 and for ~-vector Charon 4A, respectively. Plasmid DNA and RF M 13 were isolated by scaled-up alkaline minilysates methods (6) followed by CsCl ultracentrifugation.

~-vector Charon 4A and Charon 4 recombinant clones were isolated by scaled-up plate lysate methods (6).

H. olYmorpha total DNA of the size greater than 50 kb was isolated from spheroplasts as previously described (5).

Charon 4 H. polYmor~ha DNA library was constructed by ligating partially EcoRI digested H. polymorpha DNA with Charon 4 arms as described previously (5).

PolyA mRNA from H. ~olymorpha and analysis of the mRNA by an in vitro cell free rabbit reticulocyte system is described previously (5).

mRNA labelling: mRNA was partially fragmented by mild alkaline treatment (7) and labelled at the 5'-end with ,~,_32p-ATP (Amersham)-The differential plague filter hYbridisation wasperformed essentially as described in (12). Recombinant phages were plated to about 3,000 pfu per plate. Plaques from each plate were blotted into a set of 5-6 replica nitro-cellulose filters (BA85, Schleicher and Schull).
The filters were hybridized to appropriate 32P-mRNA or 32p_ DNA probes in 5 x SSPE. 50% formamide, containing additionally 150 ug/ml tRNA, 10 ug/ml poly A, 5 x Denhardt's solution, 5 ug/ml rRNA from H. polymorph isolated as described in (5, 6).

Sl ma~inq experiments were performed essentially as described by Favarolo et al. (8). S1 nuclease from NEN
at concentration 1,000 units/ml was used.

Hybrid selection technique was performed as described by Buneman et al. (9). Briefly, DNA from recombinant subclones was covalently bound to DPTE derivative of Sephacryl S-500. Total RNA was then hybridized with DNA/S-500 matrix. mRNA species not complementary to the immobilized DNA were washed out under very stringent conditions (5, 9). Hybridized mRNA was eluted with H20 at 100C. Hybrid selected mRNA was then translated in cell-free system, and the translation products analyzed by immunoprecipitation as described previously.

Sequence analYsis: Different overlapping fragments derived from the exonuclease Bal31 digestion of DNA
fragments encompassing FMDH gene were cloned into M13 phages mp9, mp8 and into plasmid pUC12, pUC13. The subcloned fragments were sequenced by Sanger et al. (10) and Maxam-Gilbert (11) methods.

. .
., Formate dehydroqenase was purified to homogeneity from methanol grown H. polymorpha cells as described elsewhere. Antibodies against FMDH, denaturated form, were raised in rabbits according to standard procedures.

Identification of mRNA species encoding FMDH In vitro translation products of total mRNA isolated from cells grown on 3% glucose (repression) or 1% methanol (induction) were analyzed on SDS-PAGE gels. Figure 1 shows the comparison of in vitro translation products of mRNA from induced (lane 1), not induced (lane 2) cells, as well as the immunoprecipitates of the first preparation with specific antibodies directed against FMDH (lane 4). In addition, the electrophoretic patterns of crude protein extracts from 1% methanol, 0.5%
glycerol/0.1% glucose (derepression) and 3% glucose cultures were compared with the electrophoretic mobility of purified FMDH (lanes 7, 8, 9 and 10 respectively).

The results obtained clearly identified the FMDH protein positionon SDS-PAGE, and indicate that FMDH protein and its mRNA are predominant species in cells grown on methanol (induction). The position of two other predominant proteins, MOX an DHAS, is also indicated.
Fig. 1 also points out that considerable expression is achieved under derepressed conditions (lane 8) and that 3% glucose represses the enzymes of methanol utilisation system. Above conclusions enabled us to isolate through sucrose gradient centrifugation mRNA fraction enriched in mRNA encoding FMDH (lane 3) in order to use it for screening procedure.

Screeninq for FMDH qene The H. polymorPha DNA bank in Charon 4 phage was screened by differential plaque hybridisation (Materials and Methods) with radioactive 32P-labelled mRNA from induced, . , - ~ 3390 1 2 not induced cells and with 32P-mRNA from a fraction enriched in FMDH mRNA (Fig. 1, lane 3). Additionally, replica filters were hybridized with 32P-DNA probes from clones encoding MOX and DAS genes (3, 5). The latter was done to identify and eliminate the clones encoding the two other strongly inducible genes. Desired phages were selected and their DNA further characterized.

Characterisations of recombinant clones The initial identification of a clone was achieved by hybrid selection t~c-hn; que, restriction mapping and establishing the size of the mRNA encoded by a given clone.

Hybrid selection DNA from Charon 4 recombinant clone JM was covalently bound to DPTE S-500 matrix, RNA complementary to JM clone was selected and its in vitro translation products analyzed. Fig. 1 shows that the hybrid selected mRNA
gives upon in vitro translation a maior eptide product of the same elecrophoretic mobility as FMDH peptide (lane 5). When peptides from lane 5 were precipitated with specific antibodies (lane 6), a major band of a size of FMDH and additional weak band are visible. In control experiment with not-induced mRNA not detectable mRNA of FMDH character was selected by this t~çhn; que. The presence of additional weak bands visible in lane 5 and 6 are probably artefacts of the used hybrid selection techn;que.

These data strongly suggest that clone JM contains FMDH
gene.

Restriction map and the size and direction of transcrition Restriction map of clone JM and its subclones is shown in Fig. 2. DNA fragments encompassing the gene were identified by hybridizing the Southern blots with 32p_ labelled induced mRNA.

8.5 kb EcoRI H. polymorpha DNA fragment from clone JM
contains a gene. A further analysis allowed to subclone the gene and its presumptive regulatory regions on HindIII/EcoRI 4.1 kb fragments in pBR325.

Sl mappinq Non-radioactive HindIII/EcoRI 4.1 kb fragment from plasmid p3Ml was isolate and annealed with induced and not-induced mRNA. The size of DNA protected by its cognate mRNA against the action of nuclease Sl was analyzed by agarose electrophoresis followed by Southern blotting and hybridization with appropriate 32P-DNA in order to visualize the fragment. Fig. 3, lane 1 shows that induced mRNA protects 1.2 kb long DNA fragment.
This indicates that the gene codes for a protein of about 35-37,000 daltons. This value was found for the FMDH
protein. Since in this MW region FMDH is the only strongly inducible protein, this result supports the identification of the gene.

3' end of the aene, transcription direction and the amount of FMDH transcript Two fragments cont~;ning the gene, 1.0 kb BamHI/PstI and 1.4 kg HindIII/BamHI, were isolated and a 3' end label was introduced at BamHI site. Only the label on the right (Fig. 3, lane 3-4), 1.4 kb HindIII/BamHI fragment was protected by annealing with mRNA indicating the direction of transcription from left to right (arrow in Fig. 2). This size of the band (lane 4) indicates that the 3' end of the gene is located 850 bp to the right of the BamHI site. This type of experiment was also used to roughly establish the amount of FMDH mRNA species in 1 339()l 2 total polyA+ mRNA isolated from of cells grown under different conditions. A known amount of 32p_3, end labelled DNA cont~;ning part of the gene was hybridized with varying amounts of mRNA. At DNA excess conditions, the radioactivity present in a band protected against S1 by a given amount of mRNA is a measure of the quantity of FMDH mRNA in the preparation. The data indicate that FMDH mRNA contributes about 7% + 1% and 3% to 4% of total polyA+ mRNA in preparation from induced and derepressed growth condition respectively. Fig. 3, lanes a, b, c, d, shows the comparison of intensity of the DNA band resulting from S1 experiments where 3 ug of DNA was hybridized with 10 ug of total polyA+ mRNA. It is also clearly visible that in mid-log phase of 3% glucose (repression) cultures, only negligible amounts of FMDH
transcript is visible whereas the same culture at stationary phase shows already considerable amounts of transcript. This is a good example of derepression phenomenon - in stationary phase, glucose is exhausted.

5' end of the gene 1.0 db BamHI/PstI fragment with a single 5' end label at BamHI yielded upon S1 mapping the multiple bands ranging from 255-265 bp (Fig. 3, lane 5). The comparison of this value with sequence data indicated that transcription starts around position -12 from the first ATG. The main band shows the start at "A" surrounded by pyrimidine track.

Nucleotide sequence The nucleotide sequence of FMDH gene and encompassing region was determined by Sanger (10) and Maxam-Gilbert methods (11). The fragments to be sequenced were generated by deleting with Bal31 DNA containing the gene.
Fig. 4 shows that all regions of the gene were sequenced several times in both directions. In case of doubts, M13 1 339()l 2 method data were corrected by data obtained by Maxam-Gilbert methods. The nucleotide sequence is presented in Fig. 5. The gene contains an open reading frame (ORF) of 1,020 nucleotides and code for a protein of 340 Da. The protein MW, calculated from these data, is 35,700 Da which agrees well with the values obtained by SDS-PAGE of purified protein. The gene was conclusively identified as FMDH by comparing the N-end of the gene as derived from DNA sequence with the data obtained by NH-end analysis of the purified protein.

5'-3' end regions In the 5'-control regulatory region of eukaryotes, a consensus sequence -3A(9)XXlAUG4GX6py was reported to be required in efficiently transcribed and translated genes (12, 13). In FMDH gene, the rule is only partly followed where the sequence -3AUC+lAUG+4AX+6A is present. The first ATG is proceeded by stop codons in all reading frames. The sequence CTATAAATA involved in eukaryotes in the initiation of transcription is found at position -40.
Other features assumed to play a role in transcriptional control in yeast S. cerevisiae like CAACAA or CACACA (12) not present in FMDH.

In most of the yeasts studied until now, the gene 3' end region contains characteristic sequences which, according to some authors, play a role in proper termination of transcription and serve as polyadenylation signals (14, 15). Zared and Sherman (16), and Bennetzen and Hall (17) assumed that a sequence T-rich...TAG...TAGT(or TATGT)...AT...TTT or T...TAAATAA...A(or G)...T...A..AT
play these roles. In FMDH gene, similarity to these consensus sequences is rarely found. When looking for some potential signals, some repeating sequences were found. Sequences TTGGA and TAGG repeat twice. AAATATAA, similar to animal polyadenylation signal, is located 30 ,, , bp downstream from the end of ORF.

Exam~le 1:
In order to be able to study the functional regions of FMDH 5' upstream region, a series of deletion of this region was isolated. First, to obtain the promoter without the structural gene, a pUC type plasmid cont~;n;ng the 1.4 kb Bam HI fragment was subjected to Bal31 exonuclease treatment after the plasmid was linearized at a proper point. At the beginning, attention was focused on the promoter fragment which had the deletion at the position -5 from the first ATG; the fragment is called n-5 promoter". Also "-9" deleted promoter was used in some experiments.

The "-5 promoter" was fused to the open reading frame of the bacterial ~-lactamase gene (Bla). The gene was used in the laboratory as a very suitable model for studying the expression of foreign protein under the control of yeast promoters.

The signal sequence of the ~-lactamase was not present in the construction obtained, thus enabling the measurement of enzyme activity in yeast protein extracts. The fused DNA fragment was cloned into the plasmid cont~;n;ng H.
polymorpha autonomously replicating sequence (HARSl) (Fig. 6,), and S. cerevisiae Ura3 gene which serves as a marker for H. ~olymorpha transformation. The amount of ~-lactamase produced in H. polymorpha transformants was measured by the enzymatic and immuno-tests. Table 1 shows the synthesis of ~-lactamase under the control of FMDH promoter in cells grown in different media (different carbon sources).

Table 1 shows that the isolated FMDH promoter is properly and stringently controlled by .i repression/derepression/induction mech~nism. The estimation of the amount of synthesized protein shows that the system of this invention is characterised by very efficient transcription and translation of the foreign protein. In the control experiment, ~-lactamase was expressed in S. cerevisiae under the control of a strong S. cerevisiae PDC (puryvat decarboxykase) promoter on 2-um plasmid (50 copies per cell). The values obtained were lower than in the case of H. polymorpha by a factor of 5-6.

TABLE 1: Production of ~-lactamase clone enzymatic test immuno-test (U/mg protein) (% of total cell protein) ____ _______ GLU GLIC Met-OH GLU GLIC Met-OH
___ ____ ___ ____ lr 45 30 4,000 15,000 - 3-4 6-8 L 5 70 10,000 28,000 - 6-8 10-12 GLU - growth on 3% glucose (repression) GLIC - growth on 1% glicerol (derepression) Met-OH - growth on 1% methanol (induction) In all cases, cells from late logarithmic phase were taken for measurement. The plasmid containing the fusion has 50-60 copies per cell.

ExamPle 2:
Expression of genes encoding Hepatitis B surface antigens (HSBAg) under the control of FMDH promoter 1. Construction of the plasmid expressing the hepatitis proteins.

Hepatitis B 1, 2 kb DNA fragment encodes a long S2-S1-S-protein (pre-s), which after processing (removal of S2-S1-part) is converted into the S-protein. Viral envelope consists of both proteins.

For our expression experiments we have used the 1, 2 kb fragment as well as a shorter part of this DNA which encodes only S-protein. The latter is also able to form antigenic pseudo viral particles.

We have inserted both hepatitis S-gene into our universal vector. As shown in Fig. 1 and scheme 1 the vector contains autonomous replication sequence (HARS), URA3 gene from S. cerevisiae as a selective marker and H.
polymorpha promoter followed by short linker. After the S-gene we have placed DNA fragment derived from H.
polymorpha MOX gene exhibiting the transcription terminator function. Fig. 7 shows the construction cont~ining the S-gene.

2. Transformation of H. polymorpha and screening for clones expressing HSBAg.

H. polymorpha URA3 mutant LR9 was transformed with the above described plasmids. The yeast transformants were then immediately screen for the expression of HBSAg using polyclonal antibodies. As an imuno-screening we have used Western blotting (peroxidase-protein A or to improve sensitivity 125J _ protein A). The screening procedure was considerably impeded by the strong cross-reactivity of the sera with H. polymorpha crude extract proteins.
We were, however, able to show the expressed antigen.

_ 1 3390 1 2 Fig. 8 shows the Western blotting Protein extracts from cells transformed with hepatitis gene grown on methanol and shows an additional antigenic band having the expected MW of S-protein. The control extract from transformants grown on glucose (repression of FMDH
promoter) do not have this band. The results shown in Fig. 8 are coming from transformants containing FMDH -9 promoter i.e. promoter derived by deleting the DNA
fragment encompassing the promoter function till position -9 from the first ATG.

We analysed also by testing S1-nuclease mapping mRNA
produced in our transformants. The resuIts indicate that transformants are producing a lot of S-gene mRNA species and that the transcription is stringently controlled by repression/derepression/induction mech~n;sm.

The above results were confirmed by positive RIA TEST of protein extracts derived from transformed cells. In the test the monoclonal antibodies directed against native S-protein were used.

Example 3:
Expression and secretion of ~-amylase from Schwanniomyces castelli in H. polymorpha under the control of FMDH
promoter.

To study the possibility of expressing in H. polymorpha a secretory protein we have chosen ~-amylase gene from yeast S. castellii. The gene encodes the 56 kd protein which in S. castellii is totally secreted into the medium; this secretory process is accompanied by glycosilation of the protein.

We have inserted ~coRI fragment encompassing the structural gene and its terminator into our expression plasmid (Fig. 9).

H. polymorpha was transformed with this plasmid and the transformants were tested for the expression and secretion of a-amylase using a starch degradation test (halo formation on starch-iodine plates) or enzyme kinetik test kit (a-amylase Merkotest A).

The results clearly show that a-amylase is produced under control of FMDH promoter. Moreover, the protein is secreted into the medium. Fig. 10 shows that in mid-log phase about 90% of the protein is secreted into the medium. Starch-iodine plate test confirmed these results (Fig. 11).

The data also show that it is possible to get a high expression level under derepressed conditions. This feature of the system is especially very valuable and important for biotechnological applications, i.e. the synthesis of foreign proteins can begin without addition of methanol as inducer simply by exhausting glucose in the medium and/or by the addition of glycerol. A system that can be handled in such an easy way be simultaneously providing a very effective expression yielding amounts of proteins applicable in the biotechnological industry has not been provided earlier.

In separate studies it has been shown that the other H.
~olymor~ha promoters like MOX and DAS do not respond so strongly to derepression signals. In the case of DAS
promoter, the expression under derepressed condition is additionally decreased by post-transcriptional control.

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Claims (31)

1. A DNA fragment characterized in that it comprises a promoter region of a gene coding for a protein derived from a methylotrophic yeast and having formate dehydrogenase (FMDH) activity, said gene being identical or equivalent to a FMDH gene being obtainable from the Hansenula polymorpha genome, wherein the FMDH gene is located on a 3.5 kb BamHI.HindIII fragment, said promoter region being derepressible when said methylotrophic yeast is grown on glycerol as an only carbon source and is inducible by addition of methanol.

2. A DNA fragment as claimed in claim 1 characterized in that the gene codes for a wild type FMDH protein.

3. A DNA fragment as claimed in claim 1 characterized in that it codes for the promoter region.

4. A DNA fragment as claimed in claim 1 characterized in that it has been modified by recombinant DNA
technologies, while retaining its promoter function.

5. A DNA fragment as claimed in claim 1, characterized in that it comprises the 5' region of the nucleotide sequence as shown in Figure 5.

6. A DNA fragment as claimed in claim 1, characterized in that it is combined with DNA-sequences encoding foreign genes so as to bring these genes under the stringent control of the regulation of the FMDH regulatory sequences.

7. A DNA fragment as claimed in claim 6, characterized in that said foreign genes are encoding:

(a) Hepatitis B Virus S1-S2-S antigen (b) Hepatitis B Virus S-antigen (c) alfa-amylase from Schwanniomyces castellii (d) glucoamylase from Schwanniomyces castellii (e) invertase from Saccharomyces cerevisiae.

8. A DNA fragment as claimed in claim 1 characterized in that it is combined with DNA-sequences coding for secretory signals.

9. A DNA fragment as claimed in claim 8 characterized in that the secretory signals are:

Hansenula polymorpha membrane translocation signals, Schwanniomyces castellii .alpha.-amylase and glucoamylase signals, or Saccharomyces cerevisiae .alpha.-factor and invertase signals.

10. A DNA fragment as claimed in claims 1, 2, 3, 4, 5, 6, 7, 8 or 9 which has been obtained from natural DNA and/or cDNA and/or chemically synthesized DNA.

11. A recombinant vector which contains DNA fragments as claimed in claim 1 or 5.

12. A micro-organism characterized in that it comprises a vector as claimed in claim 11.

13. A micro-organism as claimed in claim 12 characterized in that it is a yeast chosen from one of the genera Candida, Hansenula or Pichia.

14. A micro-organism as claimed in claim 13, characterized in that it has received a DNA-molecule as claimed in claim 1 by transformation.

15. A micro-organism as claimed in claim 14, characterized in that the DNA fragments have been integrated into the genome of the micro-organism or maintained as an extrachromosomal DNA-molecule.

16. A micro-organism as claimed in claim 15, characterized in that it tolerates high concentrations of foreign proteins.

17. A process for producing a useful substance, characterized in that a micro-organism containing a DNA
fragment as claimed in claim 6 is cultured and the substance is recovered and purified.

18. A DNA fragment as claimed in claim 6 characterized in that it is combined with DNA-sequences coding for secretory signals.

19. A DNA fragment as claimed in claim 18, characterized in that the secretory signals are:

Hansenula polymorpha membrane translocation signals, Schwanniomyces castellii .alpha.-amylase and glucoamylase signals, or Saccharomyces cerevisiae .alpha.-factor and invertase signals.

20. A DNA fragment as claimed in claim 19 which has been obtained from natural DNA and/or cDNA and/or chemically synthesized DNA.

21. A recombinant vector, which contains DNA fragments as claimed in claim 18.

22. A micro-organism characterized in that it comprises a vector as claimed in claim 21.

23. A micro-organism as claimed in claim 22 characterized in that it is a yeast selected from the genera Candida, Hansenula or Pichia.

24. A micro-organism as claimed in claim 23 characterized in that it has received a DNA-molecule as claimed in claims 18, 19 or 20 by transformation.

25. A micro-organism as claimed in claim 23 characterized in that the DNA sequences have been integrated into the genome of the micro-organism or maintained as an extra chromosomal DNA-molecule.

26. A micro-organism as claimed in claim 25 characterized in that it tolerates high concentrations of foreign proteins.

27. A process for producing a useful substance characterized in that a micro-organism as claimed in any one of claims 23, 25 or 26 is cultured and the substance is recovered and purified.

28. A DNA fragment as claimed in claim 9, wherein said Hansenula polymorpha membrane translocation signal are those from peroxisomal proteins methanol oxidase and dihydroxyacetone synthase.

29. A DNA fragment as claimed in claim 19, wherein said Hansenula polymorpha membrane translocation signal are those from peroxisomal proteins methanol oxidase and dihydroxyacetone synthase.

30. A DNA fragment as claimed in any one of claims 2 to 4, 6 to 9, 18 to 20, 28 and 29, characterized in that it comprises the 5' region of the nucleotide sequence as shown in Figure 5.

31. A DNA fragment as claimed in claim 10, characterized in that it comprises the 5' region of the nucleotide sequence as shown in Figure 5.