JPH042234B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a novel method for producing γ-endorphin by genetic recombination, and related recombinant plasmids, transformed strains, and fusion proteins. γ-Endorphin is a peptide with morphine-like physiological activity composed of 17 amino acids and has the following amino acid sequence. γ-endorphin: Try-Gly-Gly-Phe-
Met−Thr−Ser−Glu−Lys−Ser−Gln−Thr−
Pro-Leu-Val-Thr-Leu The novel recombinant plasmid pENDC1 of the present invention is
It has the DNA sequence shown in FIG. The present invention is suitable for fields such as fermentation industry and pharmaceutical industry. [Prior Art] γ-endorphin is a peptide belonging to the endorphin family that exhibits morphine-like physiological activity.
It is an interesting bioactive peptide that exhibits analgesic activity approximately 5 times that of leucine enkephalin and approximately 3 times that of methionine enkephalin. The technical background of the present invention is so-called genetic manipulation technology. However, no efficient method for producing γ-endorphin using genetic manipulation is known. As a result of modifying the E. coli-derived dihydrofolate reductase (hereinafter referred to as DHFR) gene, the present inventors have already developed a plasmid vector pTP70-1 (Japanese Unexamined Patent Application Publication No. 1983-1972) for expressing a heterologous gene.
267276) and a method for creating a fusion gene using the same (Japanese Patent Application Laid-Open No. 144992/1999). In addition, the chemistry that encodes methionine enkephalin (hereinafter abbreviated as MEK) to pTP70-1
We are developing an efficient method for producing MEK by incorporating DNA (Japanese Unexamined Patent Publication No. 1-252289). The recombinant plasmid pMEK2, which was obtained when developing an efficient MEK production method, was created using the restriction enzyme BamH.
A fusion gene with DHFR can be easily created by simply replacing the sequence between the and Xho sites with foreign DNA. Furthermore, when a fusion gene is created using pMEK2, the amount of the fusion protein obtained as a result of expression of the fusion gene is expected to accumulate in E. coli cells at approximately 20% of the total cell protein. However, there is no example of using the above expression vector for the production of γ-endorphin. [Object of the invention] The object of the present invention is to produce γ using genetic engineering techniques.
- To develop a method for mass production of endorphin. Utilizing the above knowledge and as a result of intensive research, the present inventors explained and chemically synthesized the gene encoding γ-endorphin, and by incorporating it into pMEK2, we created a fusion gene between the γ-endorphin gene and the DHFR gene. discovered that it was possible to produce a large amount of DHFR-γ-endorphin fusion protein (hereinafter abbreviated as fusion protein) by creating a fusion gene and expressing the fusion gene in Escherichia coli.
Furthermore, it was revealed that γ-endorphin can be effectively produced by using a fusion protein, and the present invention was completed. [Configuration of the Invention] The present invention provides (1) a novel recombinant plasmid pENDC1 that enables large-scale expression of fusion proteins;
E. coli cells containing pENDC1, (3) fusion protein produced by E. coli containing pENDC1, (4)
The invention consists of a method for separating and purifying a fusion protein from E. coli containing pENDC1, and (5) a method for producing γ-endorphin using the fusion protein. (1) Novel recombinant plasmid pENDC1 Figure 1 shows the entire nucleotide sequence of pENDC1 of the present invention. The figure shows that only one DNA strand sequence of a double-stranded circular DNA is contained in a plasmid.
Among the restriction enzyme C1a sites, the cleavage recognition site near the restriction enzyme Hind site, 5'-
ATLCGAT-3', counting the first "A" as number 1, is written in the direction from the 5' end to the 3' end. pENDC1 of the present invention is a novel recombinant plasmid. pENDC1 has a size of 4676 base pairs and can confer trimethoprim and ampicillin resistance to the host E. coli. pENDC1 is pMEK2 (Unexamined Japanese Patent Publication No.
Described in Publication No. 252289. ) has a structure in which the 26 base pair sequence containing the sequence encoding MEK between the BamH and Xho sites is replaced with 62 base pairs of chemically synthesized DNA containing the sequence encoding γ-endorphin. In FIG. 1, the sequence from position 533 to position 594 is derived from chemically synthesized DNA. The other sequences are pMEK2-derived sequences. The array from 57th to 590th in Figure 1 is as follows:
It encodes a fusion protein in which γ-endorphin is bound to the carboxy-terminal side of DHFR via arginine (Arg). Upstream of the sequence encoding the fusion protein, there is a sequence that allows efficient gene expression (Japanese Patent Application Laid-Open No. 63-267276). i.e. 43
The sequence from position 4634 to position 4662 is the consensus transcription promoter and contributes to efficient addition. From this, pENDC1 can produce a large amount of fusion protein when introduced into E. coli. The created fusion protein accumulates in a soluble state within the bacterial body, accounting for approximately 20% of the total bacterial body protein. This makes E. coli containing pENDC1 resistant to trimethoprim. Furthermore, pENDC1 has an ampicillin resistance gene derived from pMEK1. From this, E. coli into which pENDC1 has been introduced,
It also shows resistance to ampicillin. pENDC1 was introduced into E. coli and kept stable;
E. coli containing pENDC1 was sent to the Microtech Institute.
It has been deposited as FERM BP-2030. pENDC1 having such features can be constructed according to Example 1, but the present invention is not limited by the method for constructing the recombinant plasmid. (2) E. coli containing pENDC1 E. coli containing pENDC1 shows resistance to trimethoprim and ampicillin.
As a result of efficient expression of the fusion protein gene, E. coli containing pENDC1 accumulates a large amount of the fusion protein in a soluble state within the bacterial body. When E. coli containing pENDC1 was cultured at 37°C to the stationary phase using YT+Ap medium (liquid medium containing 5 g of NaCl, 8 g of tryptone, 5 g of yeast extract, and 50 mg of ampicillin sodium in medium 1). , the accumulated fusion protein reaches approximately 20% of the bacterial cell protein. When cultured bacterial cells are suspended in an appropriate buffer such as phosphorus buffer, disrupted by French press or sonication, and separated into supernatant and precipitate by centrifugation, all of the fusion protein is recovered in the supernatant. E. coli containing pENDC1 has been deposited with the Institute of Fine Technology as FERM BP-2030. (3) Fusion protein Figure 2 shows the DNA sequence of the part encoding the fusion protein and the amino acid sequence of the protein predicted to be made from it. The fusion protein is a novel protein consisting of 178 amino acids. Counting from the amino terminal side, 1
The sequence from position 159 to E. coli wild type
This is a sequence in which one amino acid substitution has occurred in DHFR (Cys-152 (Wild type) → Glu-152), and the sequence from positions 162 to 178 is γ-endorphin. The amino acid immediately preceding the sequence of γ-endorphin is arginine (Arg). γ-endorphin does not contain arginine. From this, the fusion protein can be specifically excised by treating it with arginylendopeptidase (available as a commercially available product). The isoleucine (I1e)-leucine (Leu) sequences at positions 160 and 161 are of pMEK2.
This sequence was created to match the open reading frame of the genetic code when introducing DNA encoding γ-endorphin into the BamH site (produced by pTP70-1, which is the origin of pMEK2).
DHFR consists of 162 amino acids, and two amino acid sequences of Gln-lle are bound to the sequence from 1 to 160, counting from the amino terminal side, of the amino acid sequence of the fusion protein shown in Figure 2. I'm doing an array. ). fusion protein and gamma
-The molecular weights of endorphin are 20 and 20, respectively.
135 and 1859. Fusion proteins are novel proteins. Although the fusion protein has a structure in which γ-endorphin is fused to the carboxy terminal side of DHFR, it has DHFR enzyme activity. For this reason, when E. coli produces large amounts of the fusion protein, it becomes resistant to trimethoprim, a DHFR inhibitor and antibacterial agent. (4) Separation and purification of fusion protein The method for separation and purification of fusion protein of the present invention is as follows:
It consists of the following steps: culture of bacterial cells, disruption of bacterial cells, DEAE-Toyopearl column treatment, mesotrixate (MTX)-conjugated affinity chromatography, and DEAE-Toyopearl column chromatography. Culture of bacterial cells Culture of E. coli containing pENDC1 is carried out using YT
+Ap medium (5 g NaCl, 8 g in 1 liter medium)
of tryptone, 5g of yeast extract and
Liquid medium containing 50 mg ampicillin sodium. ) can be cultured. In addition to this, ST+Ap medium (in 1 liter of medium,
Liquid medium containing 2 g glucose, 1 g dipotassium phosphate, 5 g polypeptone, 5 g yeast extract and 50 mg ampicillin sodium. ), any medium that allows bacterial growth can be used, but as far as we have investigated, YT+Ap medium is optimal. E. coli containing pENDC1 is inoculated into a medium and cultured at 37°C until the late logarithmic growth phase or stationary phase. The cultured bacterial cells are collected by centrifugation at 5000 rpm. From 1 liter of culture medium, 2 to 5 g of wet cells can be obtained. Bacterial collection and subsequent operations are performed at low temperatures (between 0 and 10°C, preferably 4°C) unless otherwise specified. Disruption of bacterial cells The bacterial cells obtained by culturing were suspended in buffer solution 1 (10 mM potassium phosphate buffer containing 0.1 mM sodium ethylenediaminetetraacetate (EDTA), PH 7.0) at 3 times the wet weight, Crush the bacterial cells using a French press. The cell suspension is ultracentrifuged at 35,000 rpm for 1 hour to obtain a supernatant (cell-free extract). DEAE-Toyopearl column treatment Cell-free extract was pre-treated with 50mM KCl.
Apply the column to a DEAE Toyopearl column equilibrated with buffer 1 containing 50mM KCl.
Wash the column with buffer 1 containing Oxygen elution was performed using 0.1M to 0.3M KCl using buffer 1.
The eluate is fractionated into fixed amounts using a fraction collector. Oxygen elution is performed using buffer 1 containing 0.3M KCl. Fractionate a certain amount of the eluate using a fraction collector. Measure the DHFR activity of the fractionated eluate,
Collect fractions containing enzyme activity. MTX-bound affinity chromatography The enzyme solution obtained by the above procedure is adsorbed onto an MTX-bound agarose affinity column equilibrated with buffer 1 in advance. After adsorption, add buffer 2 (0.1 m
Wash with 10mM potassium phosphate buffer containing MEDTA, pH 8.5). For washing, measure the absorbance of the eluate from the column at 280 nm, and continue to flow the same buffer until the absorbance becomes 0.1 or less.
Elution of the enzyme is performed using Buffer 2 containing 1M KCl and 3mM folic acid, and the eluate is fractionated into fixed amounts using a fraction collector. Measure the DHFR activity of the fractionated eluate, and collect the fractions containing enzyme activity.
The obtained oxygen solution is dialyzed three times against buffer solution 1. At this stage, a fusion protein with a purity of over 95% is obtained. DEAE-Toyopearl column chromatography The dialyzed oxygen solution is adsorbed onto a DEAE-Toyopearl column equilibrated with buffer 1 in advance. After adsorption, buffer 1 containing 50mM KCl
wash with Elution of the enzyme was performed using buffer 1 for 50 min.
A linear concentration gradient from mM to 0.03M KCl is used, and the eluate is fractionated in fixed amounts using a flank collector. The absorbance at 280 nm and DHFR activity of the fractionated eluate are measured. Collect fractions with a constant value of enzyme activity/absorbance at 280 nm. By the above operations, the fusion protein can be highly purified and homogenized with good reproducibility. According to the present invention, the purification of the fusion protein can be carried out within one week, including culturing the bacterial cells, and a homogeneous enzyme preparation can be obtained with a recovery rate of 50% or more. To measure DHFR enzyme activity, take the reaction solution (0.05mM dihydrofolic acid, 0.06mM NADPH, 12mM 2-mercaptoethanol, 50mM phosphate buffer (PH7.0)) into a 1ml cuvette, and add the enzyme solution to it. In addition, this is done by measuring the change in absorbance over time at 340 nm. One unit of enzyme is defined as the amount of oxygen required to reduce 1 micromole of dihydrofolate per minute under the above reaction conditions. This measurement can be easily performed using a spectrophotometer. (5) Production of γ-endorphin using fusion protein Cleavage and separation of γ-endorphin from the purified fusion protein is performed by treatment with arginylendopeptidase (available as a commercially available product). Arginyl endopeptidase was added at a ratio of 0.01 weight per 1 weight of purified fusion protein, and incubated at 37°C in 50mM Tris-HCl buffer, pH 8.5.
Medium, 24 hour processing. Add an equal volume of 50% acetic acid to the reaction solution. This sample was processed using an HPLC device (Shimadzu LC).
-4A, inertsil-ODS column), 0.1%
Elute and separate using a concentration gradient of 15% to 50% acetonitrile in trifluoroacetic acid. Eluates can be detected by measuring absorbance at 220 nm. FIG. 3 shows a high performance liquid chromatogram of a fusion protein sample treated with arginine endopeptidase. The peak approximately 20 minutes after sample injection is γ-endorphin. Separate this peak fraction. After drying the separated eluate using an evaporator, a small amount of water is added and lyophilized to remove the solvent, yielding γ-endorphin. Furthermore, the amino acid composition can be confirmed by acid hydrolyzing the obtained peptide and then performing amino acid analysis. In the example of the present invention, bacterial cells with a wet weight of approximately 11 g were obtained from the medium in step 3, and this bacterial cell (calculated approximately 252 mg of fusion protein, approximately 23.3 mg of γ
- Contains endorphin. ), approximately 132 mg of fusion protein (yield, 52%, calculated approximately 12 mg of γ
- Contains endorphin. ), of which 20 mg of the fusion protein was treated with arginyl endopeptidase and then analyzed by HPLC.
Approximately 1.3 mg of γ-
I was able to get an endorphin. [Effect of the invention] The novel plasmids pENDC1 and
By using E. coli containing pENDC1,
The fusion protein can be easily separated and purified with high yield, and it has morphine-like physiological activity because γ-endorphin can be efficiently excised from the fusion protein by treatment with a proteolytic enzyme. It is effective for the production of γ-endorphin, which is known as γ-endorphin. Next, examples of the present invention will be shown. Example 1 Creation of pENDC1 The DNA encoding γ-endorphin is 1 5'-
GATCCGCTACGGCGGTTTCATGACCTC
AG-3' 2 5'-AAAAAATCACAGACCCCGCTG-3' 3 5'-TCGAGTTATTCACCTTTTTTG-
3′ 4 5′−TATGCGTTTTGATGATTG−3′ 5 5′−GTGACTCTGTAAC−3′ 6 5′−
Six DNAs of TCGAGTTACAGAGTCACCACGGGG-3' were chemically synthesized according to the phosphoramidite method, and after purification, the 5' end of each DNA was phosphorylated using polynucleotide kinase. Approximately 0.1 ml (containing approximately 0.01 μg of DNA) of the phosphorylated DNA was taken and incubated at 60° C. to anneal both DNAs (this was referred to as DNA 1). Approximately 1 μg of pMEK2 was digested with BamH and Xho and then treated with alkaline phosphatase. By treating the alkaline phosphatase-treated DNA with phenol, the coexisting enzyme protein is denatured and removed, and then the DNA is denatured with ethanol.
was precipitated. After washing the precipitated DNA with 70% ethanol, the ethanol was removed and the precipitate was dried under reduced pressure. DNA with BamH and Xho
The operations of cleavage, alkaline phosphatase treatment, phenol treatment, and ethanol precipitation are all described in “Molecular Cloning A Loboratory.
Manual” (T. Maniatis, EFFritsch, J.
Sambrook, eds.Cold Spring Harbor
Laboratory (1982), hereinafter referred to as Document 1. ). dried
The DNA was mixed with 50μ of ligase reaction solution (10mM Tris).
-HCl, PH7.4, 5mM _MgCl2 , 10mM dithiothreitol, 5mM ATP), then 5μ
Add 1 unit of T4-DNA to this
Ligase was added and the DNA ligation reaction was carried out at 10°C for 12 hours. This reaction product was transformed using the transformation method (transformation met hod, described in the above document 1).
It was incorporated into E. coli HB101 strain according to the following. The treated cells were transferred to a nutrient agar medium containing 50 mg/ml ampicillin sodium and 10 mg/ml trimethoprim (in medium 1, 2 g glucose, 1 g dipotassium phosphate, 5 g yeast extract, 5 g polypeptone). , including 15g of agar.)
By coating on the top and culturing at 37℃ for 24 hours,
We were able to obtain 26 colonies. Select 8 colonies randomly from these colonies and add 1.5ml each.
of YT+Ap medium (in medium 1, 5 g of NaCl,
5g yeast extract, 8g tryptone, 50mg
Contains ampicillin sodium. ), 37℃,
The bacterial cells were cultured overnight. Each culture solution was placed in an Etzpendorf centrifuge tube, centrifuged at 12,000 rpm for 10 minutes, and the bacterial cells were collected as a precipitate. to this,
0.1ml electrophoresis sample preparation solution (0.0625M
Contains Tris-HCl, PH6.8, 2% sodium lauryl sulfate (SDS), 10% glycerin, 5% 2-mercaptoethanol, 0.001% bromophenol blue. ) was added to suspend the bacterial cells, and this was kept in boiling water for 5 minutes to dissolve the bacterial cells. This treated sample was subjected to SDS-polyacrylamide gel electrophoresis (UK Lammli; Nature,
vol. 227, p. 680 (1970)). As a standard sample, E. coli containing pMEK2 was treated in the same way, and as molecular weight markers, lactalbumin (molecular weight 14200), trypsin inhibitor (molecular weight 20100), trypsinogen (molecular weight 24000), carbonic anhydrase (molecular weight 29000), Samples containing glyceraldehyde 3-phosphate dehydrogenase (molecular weight 36,000), egg albumin (molecular weight 45,000), and bovine serum albumin (molecular weight 66,000) were run on a 10 to 20% polyacrylamide gradient gel. As a result, in all colonies, pMEK2
The band of the DHFR-MEK fusion protein disappeared, and a protein with a clearly larger molecular weight (estimated to have a molecular weight of about 24,000) was observed. The DHFR-MEK fusion protein of pMEK2 (molecular weight, 18963) has a molecular weight of approximately 22000 under these conditions.
It migrates as a protein. Select one strain from among these, culture it in YT + Ap medium, and use the method of Tanaka and Weisblum (T.Tanaka,
B. Weisblum; J. Bacteriology, vol.121, p.354
(1975)). The obtained plasmid was named pENDC1.
pENDC1 should have a structure in which the sequence between BamH and Xho of pMEK2 is replaced with the chemically synthesized DNA sequence. EcoR (sequences 471-476 in Figure 1) and Sal (sequences 892-898 in Figure 1) of pENDC1
About 400 nucleotides of DNA obtained by cleaving with
Enzymology, vol.101, p.20 (1983)),
The base sequence was determined. As a result, the sequence from position 471 to approximately position 898 of the sequence shown in FIG. 1 was confirmed. By examining the nucleotide sequence, pENDC1
was shown to encode the fusion protein. The nucleotide sequence of pMEK2 has been revealed by the present inventors (Japanese Unexamined Patent Publication No. 1-252288).
In addition, the approximately 4.2 kilobase pair DNA obtained by EcoR-Sal cleavage of pENDC1 is Pst,
The results of restriction enzyme cleavage experiments using Hind, Hpa, Aat, Pvu, Bgl, and Cla showed that the DNA was completely identical to the approximately 4.2 kilobase pair DNA obtained by EcoR-Sal cleavage of pMEK2. Ta. From the above results, it was determined that the entire base sequence of pENDC1 was the sequence shown in FIG. Example 2 Fusion protein produced by E. coli containing pENDC1 The amino acid sequence of the fusion protein produced by E. coli containing pENDC1 can be predicted from the base sequence of the gene. Since the first sequence from position 57 to position 590 encodes the fusion protein, the amino acid sequence was estimated using a triplet code table. As a result, the amino acid sequence shown in FIG. 2 was obtained. The endorphin fusion protein was isolated and purified from E. coli containing pENDC1, and the properties of the purified protein were investigated. Purification of fusion protein A Amount of bacterial cells used: wet weight 11 g B Enzyme purification table The purification process in the table is cell-free extract,
DEAE-Toyopearl column treatment, mesotrixate-coupled affinity chromatography,
and DEAE-Toyopearl Column Chromatography.

[Table] When the obtained enzyme protein was analyzed by SDS electrophoresis (method described in the above example),
A single protein band with a molecular weight of approximately 24,000 was shown, indicating that the obtained enzyme preparation was homogeneous. Properties of isolated and purified fusion protein When the purified protein exhibiting DHFR activity was examined by enzyme immunoassay, it was found that γ
- Shown to react with antibodies against endorphin. That is, it has been revealed that the purified protein contains a structure immunologically equivalent to γ-endorphin. In order to clarify the amino acid sequence of the carboxy-terminal side of the purified protein, carboxypeptidase Y was applied to the purified protein at varying times, and the released amino acids were quantified (using the carboxypeptidase method). Method for determining the carboxy-terminal amino acid sequence). the result,
-Val-Thr-Leu (carboxy terminal) was expected. Furthermore, when the purified protein was subjected to acid hydrolysis and then subjected to amino acid analysis, results were obtained that matched the amino acid composition expected from the base sequence. Example 3 Separation of γ-endorphin from purified and separated fusion protein 2 ml of the purified homogenized fusion protein solution obtained in Example 2 (approximately 20 mg in buffer 1, approx.
1000nmole of fusion protein), 0.2mg
of arginyl endopeptidase and incubate at 37°C.
Allow to react for 24 hours. After the reaction, add 1 ml of acetic acid. Take 0.5 ml of this (which should contain about 167 nmole of fusion protein) and inertsil-
Separation was performed using an ODS 5μm column. Elution was performed using a gradient of acetonitrile (15%) in 0.1% trifluoroacetic acid.
% to 50%). From 0 to 2 minutes, 15% acetonitrile was used, and from 2 minutes to 32 minutes, a linear concentration gradient of 15% to 50% acetonitrile was applied. As a result, an elution curve as shown in FIG. 3 was obtained. The peak fraction approximately 23 minutes after sample injection was separated, and the separated eluate was dried in an evaporator, and then a small amount of water was added and lyophilized to remove the solvent to obtain the peptide. After acid hydrolysis of the obtained peptide, one-tenth thereof was used for amino acid analysis. As a result, glutamine + glutamic acid, leucine, glycine, lysine, methionine, phenylalanine, proline, serine, threonine, tyrosine, and valine are 23.1, 24.5, respectively.
22.0, 11.5, 10.8, 11.1, 12.4, 21.7, 33.1, 10.5
and 11.5nmole were detected. The amino acid composition was consistent with that of γ-endorphin. In addition, the sample used for amino acid analysis was approximately 11.3 nmole
(approximately 21.0 μg) of γ-endorphin. These results revealed that γ-endorphin could be recovered at a yield of about 68% by using the purified homogenized fusion protein and separating the arginine endopeptidase-treated specimen using HPLC. The yield of purification of the fusion protein is approximately 52%, and the γ from the fusion protein
- Since the yield of isolation of endorphin is about 68%, it is calculated that the isolation yield of γ-endorphin produced by E. coli is about 35%.

[Brief explanation of drawings]

Figure 1 shows the entire base sequence of pENDC1, with only one DNA strand sequence of the double-stranded DNA described in the direction from the 5' end to the 3' end.
The symbols in the figure represent nucleobases, A represents adenine,
C represents cytosine, G represents guanine, and T represents thymine. The numbers in the figure indicate the first “A” of 5′-ATCGAT-3′ of the Cla cleavage recognition site that is closer to the restriction enzyme Hind cleavage recognition site among the two restriction enzyme Cla cleavage recognition sites that exist in pENDC1. It shows the number counted as the number. Figure 2 shows
FIG. 2 is a diagram showing the base sequence of the portion encoding the fusion protein present in pENDC1 and the amino acid sequence of the protein. The symbols in the figure represent nucleobases and amino acids, A for adenine, C for cytosine, G for guanine, T for thymine, Ala for alanine, Arg for arginine, Asn for asparagine, and Asp for asparagine. Acid, Cys is cysteine, Gln is glutamine, GIu is glutamic acid, Gly is glycine, His is histidine,
Ile is isoleucine, Leu is leucine, Lys is lysine, Met is methionine, Phe is phenylalanine, Pro is proline, Ser is serine,
Thr represents threonine, Trp represents tryptophan,
Tyr represents tyrosine and Val represents valine.
The numbers in the figure indicate the numbers counted starting from "A" of the ATG codon that encodes the first amino acid, methionine. FIG. 3 shows a high performance liquid chromatogram of a fusion protein sample treated with arginyl endopeptidase. The horizontal axis is the time after sample injection in minutes, and the vertical axis is 220 nm.
The absorbance of is expressed in arbitrary units. The peak indicated by the arrow is the elution peak of γ-endorphin.

Claims (1)

[Claims] 1. A novel group that is stably replicated in Escherichia coli, can confer trimethoprim resistance and ampicillin resistance to the host Escherichia coli, has a size of 4676 base pairs, and has the DNA sequence shown below. Replacement plasmid pENDC1. [Table] [Table] [Table] [Table] [Table] 2 E. coli containing pENDC1. 3. A dihydrofolate reductase-γ-endorphin fusion protein produced by E. coli containing pENDC1 and having the amino acid sequence shown below. [Table] 4 E. coli containing pENDC1 was cultured, and dihydrofolate reductase-γ-endorphin fusion protein was added using dihydrofolate reductase activity as a guideline.
Isolation of dihydrofolate reductase-γ-endorphin fusion protein, which is purified from a cell-free extract of cultured bacterial cells using mesotrixate-coupled affinity column chromatography and anion exchange column chromatography. Purification method. 5 Separate and purify the dihydrofolate reductase-γ-endorphin fusion protein produced by E. coli containing pENDC1, digest the isolated dihydrofolate reductase-γ-endorphin fusion protein with a protease, and then digest the γ-endorphin. A method for producing γ-endorphin, which comprises separating and purifying it.