IL71232A - Recombinant plasmid encoding a human interferon-gamma polypeptide process for the production thereof and microorganisms containing the same - Google Patents

Description

Ύ-inaiUJN 70 "T7D33 713 ΊΊΐρηΠ 7DJJ72mpl Ί7)3Ρ73 ΙΙΤΙΝ n777Dnn trw jATiNni77)!! , ιιυοπ7 -|77πη ,ΠΊΝ 7JI 70 RECOMBINANT PLASMID ENCODING A HUMAN INTERFERON- Y POLYPEPTIDE, PROCESS FOR THE PRODUCTION THEREOF, AND MICROORGANISMS CONTAINING THE SAME TITLE OF THE INVENTION NOVEL HUMAN INTERFERON-γ POLYPEPT Background of the Invention Interferons (referred to as IFN hereinafter) · so far known can be classified into three large groups, i.e. IFN-a, IFN-S and IFN-γ . IFN-a is mainly produced from leukocytes, IFN-3 from fibroblasts and IFN-γ from T- lymphocytes . These IFNs have been noted as biologically active substances having anti-virus activity, activating activities upon natural killer cells and macrophages, anti-tumor activity, and the like. However, the conventional methods for obtaining IFNs by isolation from leukocytes and cultured cells cannot provide them sufficiently.

Recombinant DNA technology has now been developed to the extent that the mass production of substances which are secreted only in a small amount in cells of higher animals and are hard to isolate such as IFN has become possible by using microorganisms. For example, mRNAs of IFN-8 and IFN-a were respectively isolated from cells and cDNA complementary to the mRNA was synthesized enzymatically, inserted into a suitable plasmid as a double stranded DNA and cloned in Escherichia coli [Taniguchi, et.a_l--- Proc. Jap. Acad., 55(B), 464 - 469 (1979), Nagata, et al . : Nature 284 , 316 - 320 (1980) ] .

As for IFN-γ, there has been a report that it has a stronger cell-inhibiting activity than other IFNs based on the experiment using animal cells [B.Y. Rubin and S.L. Gupta: Proc. Natl. Acad. Sci., USA , 7_, 5923 - 5932 (1980)]. Furthermore, cloning of an IFN-γ DNA into Escherichia coli and determination of its base sequence were recently reported (P.W. Gray, et al.: Nature 295 , 503 (1982)]. 71232/3 - 2 - The present inventors have made studies in order to provide a large amount of human IF -γ polypeptide using recombinant DNA technology. As a result, it has been found that a novel IFN-γ DNA with a base sequence different from that of the known IFN- γ incorporated in a recombinant plasmid is expressible in a microorganism, particularly in Escherichia coli.

The present invention provides a recombinant plasmid containing a tryptophan promoter and downstream thereof a DNA fragment encoding a human interferon-γ polypeptide having the amino acid sequence illustrated in Fig. 3.

More specifically, the present invention provides such a recombinant plasmid, which is named pGC-7 (FE M BP-497) or pGKA-2 ( FERM BP-496) .

The invention also provides a process for producing a recombinant plasmid encoding a human interferon-γ polypeptide having the amino acid sequence illustrated in Fig. 3, which comprises culturing in a medium of microorganism transformed with a recombinant plasmid according to the present invention, accumulating said interferon-γ polypeptide in the cultured cells, and recovering the interferon-γ polypeptide therefrom.

It is to be noted that the following description and examples include subject matter which is outside the scope of the invention as claimed, and only that subject matter falling within the scope of the claims as defined, or in a manner similar thereto and involving the main features as defined in the claims, is intended to be included within the scope of the invention.

In the drawings: Fig. 1 is a flow chart illustrating construction of plasmid pGC-7. Fig. 2 is a flow chart illustrating construction of plasmid pGKA-2. - 2A - 71232/1 Fig. 3 illustrates the base sequence around the human IFN-γ DNA in plasmid pGKA-2. In Fig. 3, the γ-interferon polypeptide having 166 amino acid residues is encoded by the DNA segment from TGT (CYS) to CAG (GLN).

Fig. 4 (A) illustrates the structure of plasmid pKYP-1 and (B) illustrates that of pKYP-5.

Fig. 5 is a flow chart illustrating construction of pKYP-5.

Fig. 6 is a flow chart illustrating construction of pKYP-10.

Fig. 7 (A) is a flow chart illustrating construction of pKYP-11 and (B) illustrates the structure of pKYP-12. - 3 - Detailed Description of the Invention An object of the present invention is to provide a recombinant plasmid wherein a novel IFN-γ DNA is incor-porated, a microorganism containing the plasmid, a process for producing a novel human IFN-γ polypeptide using the microorganism and the human IFN-γ polypeptide per se.

Construction of the recombinant plasmid is carried out in the following manner.

As the novel human IFN-γ DNA, pIFNy-G4 which was cloned by the present inventors is used. Escherichia coli containing pIFNy-G4 has been deposited with the American Type Culture Collection, U.S.A. under accession number ATCC 39123.

The base sequence of the IFN-γ DNA in pIFNy-G4 was determined by the method of Maxam and Gilbert [Proc. Natl. Acad. Sci. 7_4, 560 (1977)] and is illustrated in Fig. 3.

Comparison of the human IFN-ycDNA in pIFNy-G4 and the known IFN-ycDNA [P.W. Gray, et a_l. : Nature 295 , 503 (1982)] reveals the following. The first base of the triplet coding for the ninth amino acid from the M- erminal of the mature human IFN-γ polypeptide, lysine, in the known cDNA is adenine [Gray et al.: Nature 295 , 503 (1982)].

On the other hand, as the corresponding base in the pIFNy- G4cDNA is cytosine, the ninth amino acid from the N-terminal of the human IFN-γ polypeptide encoded by the pIFNy-G4cDNA is glutamine, and not lysine. Therefore, it is apparent that pIFNy-G4 codes for a novel human IFN-γ polypeptide.

Further, pIFNy-G4 has a Rsal restriction site as the 25th base is C. That is, the sequence of the 22nd to 25th bases from 5 '-terminus of the IFNy-DNA in pIFNy-G4 is GTAC and Rsal cuts the DNA at the position illustrated with the arrow (GT -AC).

Since none of the known IFN-γ genes have Rsal site in a DNA region coding for IFM-γ polypeptide, it is apparent that pIFNy-G4 contains a DNA coding for a novel human IFN-γ polypeptide.

Therefore, recombinant plasmids constructed using pIFNy-G4 are ail new recombinant plasmids.

As the plasmid to incorporate IFN-γ DNA , any plasmid can be used so long as the DMA incorporated therein can be expressed in Escherichia coli . Preferably, a plasmid wherein a foreign DNA can be inserted downstream from a suitable promoter such as trp promoter or lac promoter and the length between Shine-Dalgarno sequence (referred to as SD sequence hereinafter) and initiation site of translation is adjusted, for example, to 6-18 base pairs is employed. Preferred examples are pKYP-10, pKYP-11 and pKYP-12 ' which were constructed by the present inventors Japanese Patent Application 213193/81 (Japanese Published Unexamined Patent Application 110600/83)] . These expression vectors prepared by the method illustrated in Reference Example 1 contain tryptophan promoters (referred to as Ptrp hereinafter) .

Recombinant plasmid pGC-7 is prepared from pKYP-11 and pIFNy-G4 as illustrated in Fig. 1. That is, pIFNy-G4 is digested with PvuII and Hindlll and the digest is puri-fied by low-qelling-temperature agarose gel electrophoresis [L. 'ieslander, Analytical Biochemistry 98_, 305 (1979)].

The resulting fragment of pIFNy-G4 is inserted into pKYP-11 at the Hindlll - BamHI site to obtain pGC-7.

Thereafter, as illustrated in Fig. 2, pGC-7 is cut with BstNI and Sail and IFN-γ DNA is purified by low-gelling-temperature agarose gel electrophoresis. The IFN-γ DNA is cloned together with a synthetic DNA in the Hindlll - Sail site of the expression vector pKYP-10 harboring Ptrp to obtain recombinant plasmid pG A-2.

IFN-γ polypeptide of the present invention is prepared in the following manner.

Escherichia coli K-12 HB101 [S.N. Cohen, et ai . : Proc. Natl. Acad. Sci., 69_, 2110 (1972)] is transformed with pGXA-2 and an Escherichia coli strain containing pGKA-2 is selected from colonies resistant to amDxcillin (referred R " Ϊ to as Ap neremafter) . The Escherichia coli strain containing pGXA-2 is cultured in a medium to produce IFM-γ polypeptide in the medium.

As the medium, either a synthetic medium or a natural medium can be used as long as it is suitable for the growth of Escherichia coli and the production of IFN-γ polypeptide .

As a carbon source, glucose, fructose, lactose, glycerol, mannitol, sorbitol, etc. may be used.

As a nitrogen source, NH4C1, ( H4)2S04, casanino acid, yeast extract, polypeptone, meat extract, bactotryp-tone, corn steep liquor, etc. may be used.

In addition, nutrients such as NH2HP04, K2HPC>4, KH2P04> NaCl, MgS04, vitamine B^and MgCl2 may be used.

Culturing is carried out at pH 5.5-8.5 and at 18 - 40°C with aeration and stirring.

After culturing for 5-90 hours, the human IFN-γ polypeptide is accumulated in cultured cells. The collected cells are treated with lysozyme, disrupted by repeated freezing and melting and subjected to centrifugation. The thus obtained supernatant fluid is subjected to extraction according to a conventional method for extraction of polypeptides to recover the polypeptide.

Determination of human IFN-γ is carried out according to the method of Armstrong [J.A. Armstrong, e_t al_. : Appl. Microbiol. 21, 723 - 725 (1971)].

Certain specific embodiments of the present invention are illustrated by the following examples.

Example 1 Insertion of human IFN-γ DNA into the expression vector pKYP-11: In this example, 6 μσ of plasmid pIFNy-G4 [3.6 kilobases (referred to as Kb hereinafter)) was dissolved in 50 ul of a solution containing 20 mM Tris-HCl (pH 7.5), 10 mM MgCl2, 10 mM dithiothreitol and 50 mM NaCl. Then, 12 units each of restriction enzymes PvuII (product of Takara Shuzo Co.; the restriction enzymes hereinafter are all products of Takara Shuzo Co. , unless otherwise specified) and Hindlll were added and digestion reaction was carried out at 37°C for 4 hours. The reaction solution was heated - 6 - at 65°C for 7 minutes to inactivate the enzymes and subjected to purification by low-gelling-temperature agarose gel electrophoresis to obtain 1.2 yg of a DMA fragment containing human IFN-γ DNA of 1.3 Kb.

Separately, 4 yg of pKYP-11 was dissolved in 40 yl of a solution containing 20 mM Tris-HCl (pH 7.5), 10 m MgCl2, 10 mM dithiothreitol and 50 mM NaCl. 3 units of BamHI was added and digestion reaction was carried out at 37°C for 3 hours. The reaction solution was heated at 65°C for 5 minutes to inactivate the enzyme. Thereafter, 30 yM each of dATP, dCTP, dGTP and dTTP were added and 8 units of Escherichia coli DNA polymerase I (Klenow fragment, product of New England Biolabs, 1 yl) was added. Fill-in reaction was carried out at 15 °C for 1 hour and the reac-tion solution was heated at 68°C for 15 minutes to inactivate the DNA polymerase I. 10 units of Hindlll was added and digestion reaction was carried out at 37 °C for 3 hours, followed by heating at 65°C for 5 minutes to inactivate the Hindlll. The digestion reaction solution of the plasmid pKYP-11 was subjected to purification by low-gelling-temperature agarose gel electrophoresis to obtain about 2.5 yg of a DNA fragment of about 4.7 Kb containing Ptrp.

Then, 0.5 yg of the DNA fragment of 1.3 Kb containing human IFN-γ DNA and 1.0 yg of the DNA fragment of about 4.7 Kb containing Ptrp, which was obtained from the plasmid pKYPrll, were dissolved in 20 yl of a solution containing 20 mM Tris-HCl (pH 7.5), 6 mM gCl2, 5 mM dithiothreitol and 500 yM ATP, and 4 units of T4 DNA ligase (product of New England Biolabs) was added. Ligation reaction was carried out at 4°C for 13 hours, and Escherichia coli HB101 was transformed with the obtained recombinant plasmid mixture by conventional technique to obtain an Ap colony. A plasmid, pGC-7 illustrated in Fig. 1 was separated from the culture broth of the colony. The structure of pGC-7 was confirmed by digestion with Hindlll, BamHI, Hpal, Sail, EcoRI and Clal and agarose gel electrophoresis. Escherichia coli strain containing pGC-7 has been deposited with the Fermentation Research Institute, Agency of Industrial - - Science and Technology (referred to as FERM hereinafter) as Escherichia coli IGC-7 (FERM P-6814) (FERM BP-497) .

Exam le 2 Construction of recombinant plasmid pG A-2: In this example, 6 ug of the pGC-7 DNA obtained in Example 1 was dissolved in 50 μΐ of a solution containing 20 mM Tris-HCl (ptl 7.5), 10 mM gCl2, 10 mM dithiothreitoi and 10 mM NaCl, and 12 units of BstNI (product of New England Biolabs) was added. Reaction was carried out at 6C°C for 3 hours. Then, 150 mM NaCl and 8 units of Sail were added and digestion reaction was carried out at 37°C for 3 hours. The reaction solution was again heated at 65°C for 5 minutes to inactivate the Sail and subjected to purifi-cation by low-gelling-temperature agarose gel electrophoresis to obtain about 0.8 yg of a DNA fragment of about 1,125 base pairs (referred to as bp hereinafter) containing a large portion of the human IFN-γ DNA.

Separately, 3 ug of pKYP-10 was dissolved in 40 ui of a solution containing 20 mM Tris-HCl (pH 7.5), 10 mM MgCl2, 10 mM dithiothreitoi and 100 mM NaCl. 6 units each of Hindlll and Sail were added and digestion reaction was carried out at 37°C for 3 hours. The reaction solution was heated at 65°C for 5 minutes to inactivate Hindlll and Sail and subjected to purification by low-gelling-temperature agarose gel electrophoresis to obtain about 1.8 ug of a DNA fragment of about 4.1 Kb containing Ptrp.

The N-terminal amino acid of the mature human IFN-γ polypeptide is cystein (Cys) . In order to express mature IFN-γ DNA, it is necessary to furnish an initiation codon (ATG) just before the 5' -terminal codon TGT (Cys) and further to adjust the length between SD-sequence and ATG to a suitable length of 6-18 bp. Therefore, the following DNA linker was synthesized.

Hindlll MetCysTyrCys BstNI AGCTTATGTGTTACTGCC (18-mer) 3'ATACACAATGACGGT (15-mer) Two single chain DNAs of 18-mer and 15-mer were synthesized by a conventional tri-ester method (R. Crea, et al.: Proc. Natl. Acad. Sci . , 7_5, 5765 (1978) 3. Then, 2 yg each of the 13-mer and 15-mer DNAs were dissolved in 20 yl of a solution containing 50 mM Tris-HCl (pH 7.5), 10 mM MgCl2, 5 mM dithiothreitol , 0.1 mM EDTA and 1 mM ATP. 30 units of T4 polynucleotide kinase (product of Boehringer Mannheim) was added and phosphorylation reaction was carried out at 37°C for 60 minutes.

Then, 2 yg each of phosphorylated 18-mer and 15-mer DNAs were mixed and the mixture was heated at 70"C for 5 minutes and allowed to stand at room temperature for annealing to obtain the DNA linker having the structure given above . 0.4 yg of the BstNI - Sail fragment of 1,125 bp obtained above and derived from pGC-7 and 1.0 yg of the DNA fragment of 4.1 Kb obtained by digestion of the expression vector pKYP-10 with Hindlll and Sail were dissolved in 25 yl of a solution containing 20 mM Tris-HCl (pH 7.5), 6 mM MgCl2, 5 mM dithiothreitol and 500 yM ATP. About 0.1 yg of the DNA linker mentioned above was added to the mixture, followed by addition of 6 units of T4DNA ligase. Ligation reaction was carried out at 4°C for 17 hours. Escherichia coli HB101 was transformed using the obtained recombinant plasmid mixture by conventional technique to obtain an Ap colony. A plasmid, pG A-2 illustrated in Fig. 2 was isolated from the culture broth of the colony. The structure of pGKA-2 was confirmed by digestion with EcoRI, Clal, Hindlll, BstNI and Sail and agarose gel electrophoresis. It was confirmed by the method of Maxam-Gilbert [A.M.

Maxam, et_ al. : Proc. Natl. Acad. Sci., 7_4, 560 (1977)] that the base sequence from the SD-sequence (AAGG) to the initiation codon (ATG) in the plasmid pGKA-2 is "AAGGGTA TCGATAAGCTTATG" . - 9 - The human IFN-γ DNA in pGXA-2 is different from known DNAs in that the DNA has Rsal site and the ninth amino acid: of the human IFN-γ polypeptide encoded by the DNA is glutamine (Gin) .

Further, the synthesized DNA used above is different from the one used by P.W. Gray, e_t al. having the following structure: me tc ysty rcys A A T T C A T G T GTTATTGTC GTACACAATAACAGT in the underlined parts. Thus, pGKA-2 has a restriction site for BstNI, CCAGG, in the DNA region coding for human IFN-γ and this feature also distinguishes pGKA-2 from known plasmids. Furthermore, the length and structure between the SD sequence and ATG are important because of influence on the expression of proteins in Escherichia coli . The base sequence between the SD-sequence and ATG in pGKA-2 is apparently different from that in the known recombinant plasmid pIFN-γ trp48 (P.W. Gray, et al. ) - .

Escherichia coli containing pGKA-2 has been deposited with the FERM as Escherichia coli IGKA-2 (FERM P-6798) FERM BP-496) .

Example 3 Production of interferon by Escherichia coli IGC-7 and IGKA-2: Escherichia coli HB101 strains containing the recombinant plasmids pGC-7 and pGKA-2 obtained in Examples 1 and 2 (IGC-7 and IGKA-2, respectively) were cultured at 37 °C for 13 hours in an LG medium consisting of 10 g/1 tryptone, 5 g/1 yeast, extract, 5 g/1 NaCl and 2 g/1 glucose and adjusted to pH 7.0 with NaOH. Then, 0.2 ml of the culture medium was inoculated in 10 ml of an MCG medium (pH 7.2) consisting of 0.6% a2HP04 , 0.3% KH2P04 , 0.5% NaCl, 0.1% H4C1, 0.5% glucose, 0.5% casamino acid, 1 mM MgS04 and 4 ug/ml vitamin B^. Culturing was carried out at 30 "C - 10 - for 4-8 hours. Then, 10 ug/ml indol acrylic acid (referred to as IAA hereinafter) which is an inducer of the tryptophan gene was added and culturing was continued for an additional 2-12 hours. Cells were harvested by centrifu-gation at 3,000 rpm for 10 minutes and washed with 30 mM NaCl and 30 mM Tris-HCl (pH 7.5) buffer solution. The washed cells were suspended in 1 ml of the buffer solution mentioned above and 200 ug of lysozyme and 5 μΐ of- 0.25 M EDTA (ethylene diamine tetraacetic acid) were added. The mixture was allowed to stand at 0°C for 30 minutes.

Freezing and melting were repeated three times to disrupt the cells. The disrupted cells were centrifuged at 15,000 rpm for 30 minutes to obtain a supernatant fluid. The amount of the interferon in the supernatant was determined according to the method of Armstrong [J.A. Armstrong, et al. : Appl. Microbiol. 21_, 723 - 725 (1971)] wherein Sindvis virus was used as a virus and FL cell derived from human amnion cells was used as an animal cell. The result is shown in Table 1.

Table 1 Reference example 1 Construction of a plasmid vector having a trp promoter: (a) Purification of tryptophan transducing phage DNA: A ptrp phage, , AcI857 trpEDIO [referred to as trp ED hereinafter, G.F. Miazzari, et al.: J. Bacteriol. 133 , 1457 (1978)] was lysogenized in Escherichia coli JA 194 strain [F~, λ~ , r^~ , m^" , Atrp E5, leu6, J. Carbon, et al. : Recombinant Molecules p.355 (1977), Raven Press]. The - - resultant lysogenic strain JA 194 (Xtrp ED) was cultured at 42°C for 30 minutes .to induce Xtrp ED phages and prepare Xphage lysate. The Aphages were purified from the Xphage lysate by the cesium chloride equilibrium density gradient centrifugation of Yamakawa, et al_. : "Chemicals of Nucleic Acids I" Tokyo agaku Dojin, p.54 - 61, (1974). The Xphages were further purified by phenol treatment and chloroform treatment according to the method of Yamakawa, et al. : "Chemicals of Nucleic Acids I" Tokyo Kagaku Dojin, p. 62 - 65, (1974) . (b) Cloning of the trp promoter into a plasmid: Cloning of the trp operon from Xtrp ED phage DNA was carried out in the following manner. That is, 3 yg of Xtrp ED DNA was digested at 37°C for 2 hours with 16 units of EcoRI and 16 units of Hindlll in 20 mM Tris-riCl (pH 7.5), 75 mM NaCl, 10 mM gCl2 and 5 mM dithiothreitol . Separately, 1 ug of plasmid pBR325 DNA was digested with 2 units of EcoRI and 2 units of Hindlll by the same method as mentioned above (final volume: 30 ul) · The reactions were stopped by heating at 65 °C for 5 minutes. Then, 15 yl each of the digests were mixed and 500 uM (final concentration) ATP and 5 units of T4 DNA ligase (product of New England Biolabs) were added. The mixture was allowed to react at 4°C for 18 hours. Escherichia coli C600 SF strain [Cameron, ejt al . :. Proc. Natl. Acad. Sci. 72_, 3416 (1975)] was transformed with the plasmid mixture by the conventional method [S.N. Cohen, et al.: Proc. Natl. Acad. Sci. 69_, 2110 (1972)] and transformants resistant to ampicillin (Ap ) , resistant to tetracycline (Tc R) and sensitive to chloramphenicol (CmS ) were obtained. Plasmid DNAs were isolated from the trans-formants of Escherichia coli and cleaved with EcoRI, Hindlll and Hpal. One of the plasmid DNAs had the structure illustrated in Fig. 4 (A) and was named p YP-1.

A Taql cleavage site exists between 4 base pairs downstream from the SD sequence (AAGG) present downstream from the tryptophan promoter. By taking advantage of this fact, the plasmid pKYP-1 was digested with Taql and EcoRI - - and the digest was subjected to purification by agarose gel electrophoresis to obtain a 2.6 Kb DNA fragment containing the tryptophan promoter and SD sequence. The 2.6 Kb DMA fragment was cloned in a known vector, pBR322, by the method as illustrated in Fig. 5. That is, 8 yg of pBR322 was digested at 45°C for 60 minutes with 2 units of • TaqI in 100 μΐ of a reaction mixture comprising 10 mM Tris- HC1 (pH 8.4), 6 mM gCl2, 100 mM NaCl and 6 mM 2-mercapto- ethanol. After partial digestion with TaqI, the digest was subjected to low-gelling- temperature agarose gel electrophoresis [Lars Wieslander: Analytical Biochemistry 98 , 305 (1979)] to obtain a 4.36 Kb purified DNA fragment.

About 1.5 iq of the DNA fragment was completely digested at 37 °C for 3 hours with 3 units of EcoRI.. About 1.0 pg of a 4.33 Kb DNA fragment was recovered by the same low gelling-temperature agarose gel electrophoresis as mentioned above. Then, 12 ug of pKYP-1 DNA was partially digested with 3 units of TaqI, the digest was subjected to low-gelling- temperature agarose gel electrophoresis to obtain about 2 ug of a 8.5 Kb purified DNA fragment and the DNA was completely digested with EcoRI by the same procedure as above to obtain about 0.5 \iq of a purified 2.6 Kb DMA fragment.

Then, 0.4 iq of the 4.33 Kb DNA of pBR322 and .0.25 pg of the 2.6 Kb DNA fragment of pKYP-1 thus obtained were added to 20 μΐ of a reaction solution consisting of 20 mM Tris- HC1 (pH 7.6), 10 mM MgCl2 and 10 mM dithiothreitol . Then, •0.5 mM ATP and 4 units of T4 DNA ligase were added to the mixture and reaction was carried out at 4°C for 18 hours.

Escherichia coli C600 SF3 strain was transformed with the recombinant plasmid DNA obtained as above. The plasmids in R R the transformant having Ap and Tc were isolated. The plasmid DNA was digested with 6 restriction endonucleases , EcoRI, Hindll, Clal (product of Boehringer Mannheim GmbH), Hpal, Hindi and BamHI to analyze the structure of the plasmid. The plasmid was recognized to have the structure illustrated in Fig. 4 (B) and was named pKYP-5. - - (c) Preparation of a portable promoter from the trp promoter : The plasmid vector pKYP-5 mentioned above is applicable as a DNA introducing vector since it has a Clal site and a Hindlll site on the D A of 1 to 20 base pairs downstream from the SD sequence. However, another Clal site is present in pKYP-5 DNA besides the Clal site immediately after the SD sequence and the fragment with the trp promoter obtained by cutting pKYP-5 DNA with EcoRI and Hindlll is a little too large, i.e. 2.65 Kb. For convenience of use, pKYP-5 was improved by the process as illustrated in Fig. 6 to obtain a plasmid having a DNA fragment containing a shorter tryptophan promoter. That is, pKYP-5 DNA was digested with Hpall and Hindlll and the digest was purified to obtain a DNA fragment of about 340 bp. The fragment was inserted into the pBR322 digested with Clal and Hindlll as illustrated in Fig. 6 to obtain pKYP-10.

The structure of pKYP-10 was determined by digestion with EcoRI, Clal, Hindlll and Hpal and agarose gel electrophoresis. (d) Connection of two or more trp promoters: In order to construct a plasmid vector having a stronger promoter activity, two trp promoters were inserted into the vector. That is, the DNA fragment of about 340 bp containing the trp promoter mentioned in step (c) above was inserted into the pKYP-10 digested with Clal and Hindlll to obtain pKYP-ll as illustrated in Fig. 7 (A). The same procedure was repeated to construct pKYP-12 illustrated in Fig. 7 (B) wherein three trp promoters were connected at the same orientation. The structure of pKYP-12 was confirmed by digestion with EcoRI, Clal, Hindlll and Hpal.

Claims (8)

- 14 - 71232/3 WHAT IS CLAIMED IS:

1. A recombinant plasmid containing a tryptophan promoter and downstream thereof a DNA fragment encoding a human interferon-γ polypeptide having the amino acid sequence illustrated in Fig. 3.

2. A recombinant plasmid according to claim 1 , which is named pGC-7 (FER BP-497) or pGKA-2 (FERM BP-496).

3. A process for producing a recombinant plasmid encoding a human interferon-Ύ polypeptide having the amino acid sequence illustrated in Fig. 3, which comprises culturing in a medium of microorganism transformed with a recombinant plasmid according to claim 1 or 2, accumulating said interferon-γ polypeptide in the cultured cells, and recovering the interferon-γ polypeptide therefrom.

4. The process according to claim 3, wherein the microorganism belongs to Escherichia coli.

5. A microorganism containing a recombinant plasmid according to claim 1 or 2.

6. The microorganism according to claim 5, which belongs to Escherichia coli.

7. Escherichia coli IGC-7 (FERM P-6814) (FERM BP-497).

8. Escherichia coli IGKA-2 (FERM P-6798) (FERM BP-496). for the Applicant: WOLFF, BREGMAN AND GOLLER