.Alpha.-Amylase Gene

The present invention relates, in general, to a cloned .alpha.-amylase gene, and, in particular, to a cloned hyperthermophilic .alpha.-amylase gene and to methods of producing .alpha.-amylase using same.

Alpha-amylases are widely distributed throughout nature. The activity of .alpha.-amylase is characterized by the hydrolysis of .alpha.-1,4 glucosidic bonds in an endo-fashion, in a process known industrially as liquefaction. Due to the high viscosities and mass transfer problems, industrial liquefaction is carried out at the highest possible temperature. Typically, using the .alpha.-amylase from B. licheniformis, the starch slurry along with calcium ions are incubated at 100.degree. C. for 5 to 10 minutes then kept at 95.degree. C. for 1 to 2 hours (Ng, T. K., and W. F. Keneally in Thermophiles: General, Molecular and Applied Microbiology, T. D. Brock, ed., John Wiley & Sons, New York (1986)). This process is essential for several industries. Glucopolymers with varying degrees of polymerization are utilized in papermaking, textile preparation, brewing and fermentation. Liquefaction is a preliminary step in saccharification by which large quantities of D-glucose can be produced from inexpensive sources.

Thermostable .alpha.-amylases are well suited for the elevated temperatures used in industrial liquefaction in that the more thermostable the enzyme, the more efficient the hydrolysis at extreme temperature. The enzymes isolated from thermophilic microorganisms display inherent thermostability comparable to their optimal growth temperature. Thus, the higher the optimal growth temperature of the microorganism, the greater the likelihood that it will produce an .alpha.-amylase suitable for industrial application.

Many .alpha.-amylases have been purified which display thermostable characteristics. These range from moderate thermophiles, with optimal enzymatic activities within the range of 50.degree. to 80.degree. C. (Antrankian, Applied Biochem. Biotech. 20/21: 267 (1989), Glymph and Stutzenberger, Applied Environ. Microbiol., 34: 391 (1977), Hasegawa et al, J. Biochem, 79: 35 (1976)), to hyperthermophiles with optimal activities above 80.degree. C. (Schumann et al, FEBS, 282: 122 (1991), Koch et al, Arch. Microbiol, 155: 572 (1991), Laderman et al (1992)). .alpha.-Amylases isolated from microorganisms with optimal growth temperatures at or near 100.degree. C. have been found to have optimal activities at this temperature, with residual activity at temperatures as high as 120.degree. C., making them ideally suited for industrial application.

Using genetic engineering technology, it is theoretically possible to clone genes and produce the enzymes that they encode in quantities sufficient for industrial application. A number of genes coding for thermophilic .alpha.-amylases have been isolated and subsequently expressed in E. coli and B. subtilis (Fukusumi et al, Eur. J. Biochem., 98: 95 (1985), Tsukagoshi et al, Mol. Gen. Genet., 195: 58 (1984), Tsukagoshi et al, J. Bacteriology, 164: 1182 (1985)). The temperature at which the genes are endogenously translated does not seem to have an effect on the expression in transformation competent cells. Thus it is possible to produce thermophilic enzymes in host cells grown at ambient temperature. However, no genes coding for hyperthermophilic .alpha.-amylases have ever been successfully cloned.

The hyperthermophilic archaebacterium Pyrococcus furiosus has been isolated from solfateric mud and found to have an optimal growth temperature of 100.degree. C. (Fiala and Stetter, Arch. Microbiol., 145: 56 (1968)). .alpha.-Amylase activity from P. furiosus has been detected in the cell-free supernatant (Antrankikian et al, WO 90/11352, (1990)), and in crude cell extract (Brown et al, Appl. Environ. Microbiol., 56: 1985 (1990)). The .alpha.-amylase derived from this bacterium is known to be stable at high temperature and is expected to be widely used in industrial fields. However, methods for the industrial production of this enzyme from P. furiosus are not established and neither the gene structure nor the amino acid sequence of this enzyme has been reported.

The present invention provides, for the first, time a cloned sequence encoding a hyperthermophilic .alpha.-amylase. The availability of this sequence makes possible the industrial scale production of this enzyme.

The present invention relates to an isolated DNA segment having a nucleotide sequence that encodes .alpha.-amylase, specifically, a hyperthermophilic .alpha.-amylase. The invention further relates to a recombinant method of producing hyperthermophilic .alpha.-amylase. The invention also relates to an expression vector suitable for use in such a method.

It is a general object of the invention to provide a gene encoding a hyperthermophilic .alpha.-amylase.

It is a specific object to provide a gene encoding .alpha.-amylase from P. furiosus.

It is another object of the invention to provide a recombinant DNA molecule comprising a vector and the above-described gene, and to provide a host cell containing same.

It is a further object of the invention to provide a method of producing hyperthermophilic .alpha.-amylase.

Additional objects and advantages of the invention will be clear from a reading of the description that follows.

FIG. 1: Nucleotide sequence of the PstI-HindIII fragment carrying the .alpha.-amylase gene (SEQ ID NO: 1). Sequences of the primer 1 and primer 2 are underlined. The amino acid sequence which was coincident with that deduced from the nucleotide sequence of the amplified fragment is encompassed by a square. The .alpha.-amylase produced in E. coli cells carrying pKENF-NH has two additional residues, Met and Gly, at the amino terminus (SEQ ID NO: 2) of its counterpart purified from the cell extract of P. furiosus (SEQ ID NO: 8) because of the introduction of the recognition sequence of NcoI in the expression vector.

FIG. 2: Restriction map of the PstI fragment encoding the .alpha.-amylase

FIG. 3: Structure and construction of an expression plasmid pKENF-NH

The invention relates to an isolated DNA segment encoding all, or a portion, of .alpha.-amylase from a hyperthermophilic bacteria, preferably an archaebacterium, most preferably P. furiosus. The invention also relates to a recombinant molecule containing such a DNA segment, and to cells transformed therewith. In a further embodiment, the present invention relates to a method of producing hyperthermophilic .alpha.-amylase.

The DNA segment to which the invention relates, which can be a cDNA sequence, can encode the entire amino acid sequence given in FIG. 1 (the specific DNA sequence given in FIG. 1 being only one example), or a portion thereof of at least 15 amino acids (corresponding to 45 nucleotides), preferably at least 25 amino acids (corresponding to 75 nucleotides), more preferably at least 35 amino acids (corresponding to 105 nucleotides), and most preferably at least 75 amino acids (corresponding to at least 225 nucleotides). One skilled in the art will appreciate that these portions have utility, for example, as probes. DNA segments to which the invention relates also include those encoding proteins (or polypeptides) having substantially the same enzymatic activity of .alpha.-amylase of P. furiosus (for example, functionally equivalent allelic or species variations of the amino acid sequence of FIG. 1).

The present invention also relates to a recombinant DNA molecule that includes a vector and a DNA segment as described above (advantageously, a DNA segment encoding the protein shown in FIG. 1). The vector can take the form of a virus or a plasmid vector. Examples of such vectors include, for example, derivatives of the .lambda. phage or of the pUC plasmid (e.g. pUC18 and pUC 19) and pET vectors. The DNA segment can be present in the vector operably linked to regulatory elements, including, for example, a promoter (for example, a heat shock promoter). Promoters appropriate for use in the present method include promoters functional in eubacteria, for example E. coli or B. subtilis, or in eucaryotes, for example, yeasts. The recombinant molecule of the invention can be suitable for transforming procaryotic or eucaryotic cells.

In a further embodiment, the present invention relates to a host cell transformed with the above-described recombinant molecule. The host can be procaryotic (for example, bacterial, such as E. coli and B. subtilis), lower eucaryotic (i.e., fungal, including yeast) or higher eucaryotic (i.e., mammalian). Transformation can be effected using method known in the art. When the recombinant molecule takes the form of an expression system, the transformed cells can be used as a source for the above-described protein.

The Examples that follow make reference to the hyperthermophilic bacteria, P. furiosus (deposited at Deutsche Sammlung von Mikroorganismen with the identification number of DSM 3638). The procedures for cloning the .alpha.-amylase gene from this bacteria and for preparing transformants carrying the gene, can be described in general terms as follows:

1. .alpha.-Amylase is purified from a cell extract of P. furiosus.

2. Partial amino acid sequences of the enzyme obtained in step (1) above is determined by the Edman method.

3. Chromosomal DNA is extracted from P. furiosus.

4. Oligodeoxyribonucleotide primers are synthesized for gene amplification based on the amino acid sequences obtained in step (2) above, and amplification by PCR is carried out using two of these primers and chromosomal DNA obtained in step (3) above as a template.

5. Chromosomal DNA obtained in step (3) above is digested with an appropriate restriction enzyme; the digest is separated by agarose gel electrophoresis, and transferred to a membrane. The amplified DNA obtained in step (4) is labeled and hybridization is carried out. DNA fragments (the sizes of which are estimated from the hybridization) are recovered from the gel.

6. Vector DNA is cut with an enzyme at a unique site and the DNA fragments obtained in step (5) above are inserted.

7. The DNA fragments inserted into the vector are introduced into a host cell and a transformant carrying the target sequence (sequence encoding the .alpha.-amylase) is selected.

8. Plasmid DNA is extracted from the transformant selected in step (7) above.

9. The sequence encoding .alpha.-amylase is operably linked to the translation signal (SD sequence) of a plasmid to construct an expression plasmid, from which translation occurs in the proper reading frame.

10. A 3'-noncoding sequence from the expression plasmid obtained in step (9) above is removed to produce another expression plasmid with higher expression level.

11. A host cell is transformed with the expression plasmid obtained in step (10) above.

12. The transformant obtained in step (11) above is cultured and .alpha.-amylase prepared from an extract of the cultured cells.

Purification of .alpha.-amylase from P. furiosus (DSM No. 3638) can be accomplished using the method of Laderman et al (1992), the technique entailing a series of successive chromatographic separations followed by reparative electroelution.

The .alpha.-amylase prepared by this method is a homodimer with a molecular weight of 130 kDa. The enzyme has a pH optimum within the range of 6 to 8 at 92.degree. C., and displays significant activity and stability independent of calcium ions. Following incubation at 100.degree. C. for three hours, the enzyme retains over 80% of its original activity.

Partial amino acid sequence information was obtained from purified .alpha.-amylase using the automated Edman method (Hunkapiller et al, Methods in Enzymology 91: 399 (1983). The N-terminal sequence of the intact protein is set forth below in Table 1 and is designated Sequence 1. The N-terminal sequence of one of the purified fragments, followed cyanogen bromide and trypsin digestion, is set forth in Table 1 and is designated Sequence 2.

Chromosomal DNA of P. furiosus can be extracted from a stationary culture of the organism at 100.degree. C. Extraction, purification, and restriction enzyme digestion can be performed with methods known in the art and detailed in Molecular Cloning, A Laboratory Manual (Maniatis et al, Cold Spring Harbor Laboratory 1982, pages 75 to 178).

Primers 1, 2, and 3 in Table 2 below, were utilized in the cloning of the .alpha.-amylase gene. The primers were designed based on the partial amino acid sequence information obtained by the Edman method. It was found that a DNA fragment could be specifically amplified when the two-step PCR (nested PCR) was performed using these primers and chromosomal DNA of P. furiosus as a template. The nucleotide sequence of the amplified fragment (FIG. 1) was identified, and possible amino acid sequences, which could be encoded by the fragment, were deduced. The amino acid sequence of sequence 1 (Table 1), which was obtained by the Edman method, was found in one of the amino acid sequences deduced. Thus the DNA fragment encoding the .alpha.-amylase amylase gene was cloned using the amplified DNA fragment as a probe.

The method of cloning the .alpha.-amylase gene can be described generally as follows.

Southern hybridization is performed and the restriction enzyme map of the chromosomal DNA surrounding the coding sequence of the .alpha.-amylase gene established using PstI, HindIII, XhoI, and EcoRI to digest chromosomal DNA of P. furiosus. Based on the restriction map obtained (see FIG. 2) a restriction fragment containing the entire .alpha.-amylase gene can be obtained and inserted into a plasmid vector. For this purpose, any of a number of available plasmid vectors can be used, for example, pUC18, pUC19, pTV118N, and pTV119N. Methods of insertion are known in the art.

Wild type or genetically modified strains of, for example, Escherichia coli, can be used as a host. However, it is preferable to use a strain that is deficient in restriction and normal in modification (r.sup.-, m.sup.+). DNA can be introduced into a host using a known method, such as that described at page 250 of Molecular Cloning A Laboratory Manual, referenced above. E. coli cells carrying the plasmid DNA (transformants) can be selected based on a marker gene present in the vector used. For example, when pTV118N is used as a vector, cells carrying the plasmid can be obtained by selection of colonies that are resistant to ampicillin.

Next, transformants carrying the .alpha.-amylase gene are selected. Selection is done either by colony hybridization or plaque hybridization according to the characteristics of the vector used, as is known in the art.

The procedures described above were followed, and a plasmid that had a PstI fragment carrying the entire .alpha.-amylase gene was obtained and inserted at a PstI site in the expression vector pTV118N. This plasmid is referred to below as pKENF.

E. coli was the host used as in the cloning studies described herein, but in principle any methophilic or even thermophilic bacteria, transformed with an appropriate vector, can be used as a host, for example Bacillus subtilis or Bacillus brevis.

Construction of an expression vector requires identification of the nucleotide sequence of the fragment carrying the .alpha.-amylase gene (FIG. 1). The recognition sequence of NcoI can be introduced near the 5'-end of the .alpha.-amylase gene such that the ATG initiation codon in the recognition sequence of NcoI is in frame. This process of site-directed mutagenesis can be done in a conventional way by use of either Mutan.TM.-K or Mutan.TM.-G (commercial products of Takara Shuzo), or can be done using PCR. In the studies involved in the present invention, Mutan.TM.-K was used to introduce the recognition sequence of NcoI in pKENF, giving pKENF-2N. The sequence between by the two NcoI recognition sequences, one on the vector sequence and another near the 5' end of the fragment of the .alpha.-amylase gene, can be deleted to obtain an expression plasmid; pKENF-N is such a plasmid. Expression from the .alpha.-amylase gene can be induced by IPTG when this gene is transcribed under the control of the promoter of lacZ gene.

In the studies that resulted in the present invention, a noncoding region of pKENF-N at the 3'-site of the .alpha.-amylase gene (between two HindIII sites) was deleted to obtain another expression plasmid with higher expression level. This expression plasmid is referred to as pKENF-NH below. Structures and a scheme for construction of plasmids pKENF, pKENF-2N, pKENF-N, and pKENF-NH are shown in FIG. 3.

E. coli cells carrying pKENF-NH were cultured, and a cell extract was obtained. Significant levels of .alpha.-amylase activity were found in the extract after heat treatment (100.degree. C.) for 10 min. No activity was detected in the cell extract obtained from E. coli cells carrying the expression vector pTV118N.

E. coli JM109 cells were transformed with pKENF-NH and a vigorously growing transformant was deposited on Mar. 7, 1992, under the terms of the BUDAPEST TREATY, in the Fermentation Research Institute, Agency of Industrial Science and Technology, Japan with the name being Escherichia coli JM 109/pKENF-NH, Accession number FERM BP-3782.

Three hundred units of extremely thermostable .alpha.-amylase measured by the Caraway method (see below) were obtained from one milliliter of the culture of E. coli JM109/pKENF-NH, thus making possible production of the enzyme on an industrial scale.

Certain aspects of this invention will be explained in greater detail by reference to the following non-limiting Examples.

Bacteria were grown on a complex medium modified from that previously described by Blumentals et al. (Blumentals et al Applied and Environ. Micro. 56(7): 1992 (1990)) consisting of artificial seawater supplemented with 0.3% tryptone, 0.7% yeast extract, and 0.1% soluble potato starch. Medium was prepared and dispensed into two liter bottles and then autoclaved. Following sterilization, in addition to the supplemental salts described previously, elemental sulfur and sodium sulfite were added at 156 mM and 2 mM, respectively. Prior to cooling to below 90.degree. C., the medium was purged with nitrogen, 1% volume of inoculum from a previously grown culture was added, and the bottles were sealed. The cultures were allowed to incubate at a constant temperature of 98.degree. C. for 16 hours and were subsequently harvested. A typical volume of growth medium used for each incubation was 20 liters, providing cell yields of 0.7 to 1.0 g/liter (wet weight).

Purification was carried out as follows

(A) Crude Extract. Cells were harvested from growth media at 7,000.times. g for 10 minutes (8000 RPM in a Beckman JA10 rotor). The supernatant was decanted and the pellet collected. The cells from 20 liters of growth medium were resuspended in a final volume of 15 ml of 50 mM sodium phosphate pH 5.5 and subsequently disrupted by sonication using a Sonifer Cell Disrupter, at 50% maximum intermittently for three minutes. The cytosolic fraction of the lysate was collected after ultracentrifugation at 95,800.times. g for 1 hour (35,000 RPM in a Beckman Ti 45 rotor). All subsequent purification procedures were carried out at room temperature; protein solutions were stored at 4.degree. C.

(B) Ion Exchange #1. The cytosolic fraction was applied to a Q-sepharose column (1.5 cm in diameter with a bed height of 45.5 cm) preequilibrated with 50 mM sodium phosphate pH 5.5 (Buffer A). Under these conditions, the amylase activity bound to the column and was eluted using 50 mM sodium phosphate pH 5.5, 1M NaCl (Buffer B) with a 200 minute linear gradient (100% A to 100% B). Fractions were collected and the tubes containing amylase were identified by activity and pooled.

(C) Ion Exchange #2. The pooled sample was diluted with an equal volume of buffer A and reapplied to the column which had been reequilibrated with 85% buffer A, 15% buffer B. The sample was eluted with the buffer described above using a 195 minute linear gradient (85% A, 15% B to 40% A, 60% B). The fractions were again pooled based upon activity and dialyzed overnight against 50 mM sodium carbonate pH 10.3 (Buffer A').

(D) Ion Exchange #3. The dialyzed sample was applied to a Q-sepharose column (1.5 cm diameter with a bed height of 46.5 cm) preequilibrated with buffer A' and eluted with 50 mM sodium carbonate pH 5.5, 1M NaCl (Buffer B') utilizing a 200 minute linear gradient (100% A' to 100% B'). Fractions containing .alpha.-amylase activity were collected and pooled. The active pool was then concentrated in Centricon 30 microconcentrators at 3020.times. g (5000 RPM in a Sorvall SS34 rotor), in 20 minute intervals, until the total volume was less than 2 ml.

(E) Electroelution. Purification was completed by electroelution from native-PAGE using the Bio-Rad model 491 Prep Cell. The apparatus was assembled using the 28 mm inner diameter gel tube containing an 8% acrylamide gel, 6 cm in height with a 1 cm, 4% stacking gel prepared as described above. The cooling buffer flow was maintained at 100 ml/min; the continuous elution flow was approximately 1 ml/min. The sample was prepared in 2.times. native sample buffer and was loaded in a volume less than or equal to 2.5 ml. Electrophoresis was carried out at 40 mV constant current and fractions were collected at 2.5 minute intervals. The elution of the protein was monitored with an Isco flow-through absorbance detector at 280 nm, allowing the correlation of specific fractions collected with the elution of protein bands from the gel. .alpha.-Amylase-containing fractions were detected by activity and screened, using silver stained native-PAGE, for purity. The active fractions, shown to be pure with the level of resolution of the silver stain, were pooled as final product. To obtain partial amino acid sequences, purified enzyme was digested with cyanogen bromide and, following reduction and pyridylethylation, with trypsin, using a modification of the methodology of Stone et al (Stone et al Practical Guide to Protein and Peptide Purification for Microsequencing, Ed. Matsudaira, P.T. Academic Press, N.Y., pp. 33-47 (1989). The resulting fragments were then separated by gradient elution from 100% water containing 0.1% (v/v) trifluoroacetic acid (TFA) to 70% acetonitrile containing 0.1% (v/v) TFA on a Aquapore RP-300 reverse phase narrow-bore column (0.2 cm .times.25 cm), utilizing a Dionex Al-450 BioLC system.

Amino acid sequence analysis was performed on a Porton Instruments Model 2020 off-line sequencer using standard program #1. PTH amino acid analysis was carried out on a Beckman System Gold system using a modified sodium acetate gradient program and a Hewlett-Packard narrow-bore C-18 column.

P. furiosus cells were grown in 2L of culture medium as described in Example 1. The cells were harvested and suspended in 4 ml of a mixture containing 25% sucrose and 0.05M Tris-HC1 (pH 8.0). Then 800 .mu.l of lysozyme (5 mg/ml) was added to the suspension. After incubation of the mixture for 1 hour at 20.degree. C., 24 ml of SET solution (150 mM NaCl, 1 mM EDTA, and 20 mM Tris HCI (pH 8.0)) was added to it. Four milliliters of 5% SDS and 400 .mu.l of proteinase K (10 mg/ml) were added, and the mixture was incubated for 1 hour at 37.degree. C., was extracted with phenol-chloroform, and precipitated with ethanol. DNA was recovered by winding with a sterilized toothpick. These steps gave 3.2 mg of genomic DNA.

Five hundred ng of P. furiosus chromosomal DNA were used as the template with 100 pmol of primer 1 and 100 pmol of primer 3 (see Table 2). The PCR profile was 94.degree. C. for 0.5 min, 40.degree. C. for 2 min, and 72.degree. C. for 2 min. Amplification was done for 35 cycles in a total volume of 100 .mu.l. One .mu.l of the reaction mixture was reamplified with primer 2 (see Table 2) and primer 3. The PCR profile was same as above, but the number of cycles was 30. Five microliters of this mixture was analyzed by agarose gel electrophoresis. A DNA fragment about 1 kilobase pairs long was specifically amplified. The amplified DNA fragment was given blunt ends and subcloned into the HincII site of pUC 18. The cloned plasmid was sequenced by the dideoxy method.

Five-.mu.g portions of P. furiosus chromosomal DNA were digested with PstI, HindIII, or EcoRI and electrophoresed through an agarose gel. The DNA was transferred to a nylon membrane and hybridized to the DNA probe obtained in Example 3. The probe was radiolabled by the random primer method. Hybridization was done for 2 hours at 65.degree. C. in a hybridization bag containing 6.times. SSC, 0.1% SDS, 5.times. Denhardt's solution, 100 .mu.g/ml calf thymus DNA, and 1.times.10.sup.7 cpm/ml of .sup.32 P-labeled probe. The membrane was washed for 40 min in a solution of 2.times. SSC and 0.1% SDS at 65.degree. and then for 20 min in a solution of 0.5.times. SSC and 0.1% SDS at 65.degree.. X-ray film was exposed to the membrane overnight to obtain an autoradiographic image. The PstI fragment 5.3 kb long, the HindIII fragment 3.1 kb long, the XhoI fragment 5.3 kb long, and the EcoRI fragments 0.7 kb and 2.4 kb long were found to be positive.

For cloning of the 5.3-kb PstI fragment obtained in Example 4, 50 .mu.g of P. furiosus chromosomal DNA was digested with PstI. The digest was separated by agarose gel electrophoresis, and DNA fragments about 5.3 kb long were purified from the gel. Plasmid pTV118N was digested with PstI and dephosphorylated, and the DNA fragments about 5.3 kb long were ligated to the plasmid DNA with T4 DNA ligase. The ligation mixture was used to transform E. coli JM109 cells. Recombinant plasmids containing the target sequence were screened for by colony hybridization. Briefly, 349 colonies were transferred to nylon membrane. The colonies were lysed with 0.5N NaOH and 1.5M NaCl and the membrane was neutralized with 1M Tris-HC1 (pH 7.0) containing 1.5M NaCl. Then the DNA was fixed to the membrane by ultraviolet irradiation. Preparation of the DNA probe and the conditions of hybridization were as described in Example 4. The plasmid obtained from one of the three positive clones was designated pKENF.

FIG. 3 shows the process of construction of the plasmid pKENF-HN. First an NcoI site was created near the translation initiation codon of the .alpha.-amylase gene in the plasmid pKENF obtained in Example 5 with use of a kit (site-directed mutagenesis system Mutan.TM.-K; Takara Shuzo). This plasmid (pKENF-2N) was digested with NcoI and self-ligated to eliminate an extra 5'-noncoding region. The resulting plasmid (pKENF-N) was digested with HindIII and self-ligated to delete a 3'-noncoding region. This recombinant plasmid was designated pKENF-NH.

E. coli JM109 cells carrying this plasmid were named E. coli JM109/pKENF-HN and were deposited at the Fermentation Research Institute, Agency of Industrial Science and Technology, Japan, as FERM BP-3782.

E. coli JM 109/pKENF-NH cells obtained in Example 6 were grown for 15 hours at 37.degree. C. in 5 ml of L broth containing 100 .mu.g/ml ampicillin. The cells were then collected from 1 ml of the culture, suspended in 200 .mu.l of a lysis solution (50 mM Tris-HCI (pH 7.6), 2 mM mercaptoethanol, 10% glycerol, 4 mM p-amidinophenyl-methanesulfonyl fluoride, and 0.1 mg/ml lysozyme), and incubated for 60 min at 37.degree. C. The mixture was then sonicated and centrifuged. The supernatant was incubated for 10 min at 99.degree. C. and centrifuged again. This supernatant was used as the crude cell extract.

e-Amylase activity was measured following Caraway, W. T. (American Journal of Clinical Pathology, 32: 97-99, 1959) with an amylase assay kit (Amylase Test Wako; Wako Pure Chemicals, Japan). Briefly, 20 .mu.l of the crude cell extract obtained as described above was added to 1 ml of the buffer containing soluble starch, which had been pre-warmed for 5 min at 90.degree. C. After incubation at 90.degree. C., the reaction mixture was mixed with 1 ml of a chromogenic reagent and 5 ml of distilled water. The absorbance at 660 nm was measured and the .alpha.amylase activity (Caraway unit) was calculated with the following equation:

where ES is a measured value when a sample solution is used and EB1 is that when distilled water is used in place of the sample solution (enzyme blank). From 1 ml of the culture medium, 300 units of .alpha.amylase was obtained.

The contents of all references cited hereinabove are incorporated herein by reference.

One skilled in the art will appreciate from a reading of this disclosure that various changes can be made in form and detail without departing from the true scope of the invention. In this regard, one skilled in the art will appreciate that the concept of placing a gene sequence derived from P. furiosus under control of a promoter distinct from the P. furiosus endogenous promoter can be applied to sequences encoding P. furiosus proteins other than .alpha.-amylase, including, for example, sequences encoding pullulanase, .alpha.-glucosidase, .beta.-glucosidase and proteases. In so doing, it is expected that expression of P. furiosus proteins can be obtained in, for example, species of Escherichia and Bacillus.