NOVEL PROMOTER

Abstract: Disclosed is a novel promoter wherein a 5′ flanking region of a promoter (referred to as promoter A) is replaced by a 5′ flanking region of another promoter (referred to as promoter B) or a chemically synthesized DNA fragment. The promoter is constructed by replacing a region existing up­ stream from the "-35" region of promoter A by the "-35" region of promoter B or a chemically synthesized DNA fragment.

Description: Background of the Invention By the development of recombinant DNA technique in recent years, mass production of heterogeneous proteins has become possible using microorganisms, particularly Escherichia coli. Improvement of the efficiency of expression of heterogeneous genes in host cells is an important subject. Specifically, in order to elevate transcription efficiency, as a promoter, i.e. a genetic information necessary for the initiation of transcription, the lactose (lac) promoter (referred to as lac promoter hereinafter), the tryptophan (trp) promoter (referred to as trp promoter hereinafter) and the like have been employed. Further, a hybrid promoter (tac promoter) of trp promoter and lac promoter has been designed. These promoters are used for the expression of heterogeneous genes (K. Itakura et al. Science 198, 1056-1063 (1977), D.V. Goeddel et al., Nature 287, 411-416 (1980), H.A. deBoer et al., Proc. Natl. Acad. Sci. USA 80, 21-25 (1983). The region which is recognized by the RNA polymerase and to which the RNA polymerase binds to initiate transcription is called "promoter". It is well known that transcription efficiency depends on the nucleotide sequence of the "promoter". According to the conventional numbering system of DNA base sequences, the promoter of Escherichia coli comprises the region around "-35", which is usually called "-35" region, the region around "-10", "which is called "-10" region or Pribnow box, and the region of "+1", i.e. transcription initiation site which is a purine base such as adenine and guanine in most promoters. The "-35" region is defined as a recognition site of the RNA polymerase. According to the statistical analysis of the nucleotide sequences of various Escherichia coli promoters, it turned out that the consensus sequence is TGTTGACANTTT, wherein A is adenine, T is thymine G is guanine, C is cytosine and N is any of A,T, G and C. The most frequently appearing part of the consensus sequence is TTGACA. On the other hand, it was found that the "-10" region is a. RNA polymerase binding site and the consensus sequence thereof is TATAATG (M. Rosenberg & D. Court, Ann. Rev. Genet. 13, 319 (1979)). As a promoter for expression of a eucaryotic gene, the lac UV5 promoter (F. Fuller, Gene 19, 43 (1982) ), or the trp promoter can be used (G.N. Bennet et al., J. Mol. Biol. 121, 113 (1978), D.V. Goeddel et al., Nature 287, 411 (1980)). In case of the lac UV5 promoter, the "-10" region (TATAATG) is completely identical with the consensus sequence of the "-10" region of the Escherichia coli promoter described above whereas the "-35" region (GCTTTACACTTT) is not identical with the consensus sequence. Reversely, in case of the trp promoter, the "-35" region (TGTTGACAATTA) is almost identical with the consensus sequence but the "-10" region (TTAACTA) is not identical with the consensus sequence. H.A. deBoer et al. of Genentech Inc. constructed a hybrid promoter by ligating a DNA fragment containing the "-35" region of the trp promoter and the 5' flanking region thereof to a DNA fragment containing the "-10" region of the lac promoter and the lac operator. Thus the advantageous properties of the trp promoter and the Lac UV5 promoter were combined. The hybrid promoter was designated as tac promoter and was employed to express a gene coding for the human growth hormone. The tac promoter is characterized in that the "-35" region derived from the trp promoter and the "-10" region derived from the Lao promoter are combined to operate as a single promoter. Both regions are almost identical with the consensus sequences (H.A. deBoer et al., Proc. Natl. Acad. Sci. USA 80, 21 (1983)). It was proved that the tac promoter has a transcriptionactivity which is about 3.5 times higher than that of the trp promoter and 2-3 times higher than that of the lac promoter. Additionally, H.A. deBoer et al . constructed a rac promoter which is a hybrid promoter of the promoter of the ribosomal RNA operon (Known as an extremely strong promoter) and the lac promoter for use in expression of a gene coding for the human growth hormone (Japanese Published Unexamined Patent Application No. 194790/82). Thus H.A. deBoer et al. provided a method for the construction of novel hybrid promoters by ligating selectively and functionally the DNA fragment containing the 5' flanking region and the "-35" region to the DNA fragment containing the "-10" region. The intention of this method is to combine the advantageous properties of both of the promoters. The method may be useful for the construction of hybrid promoters which have a high transcription activity and the ability of expression control. However, this method is not suitable for the construction of promoters which make best use of the transcription ability of Escherichia coli. According to the present invention the transcription activity of the trp promoter and the tac promoter is elevated. H.A. deBoer et al. demonstrated that the following factors affect the strength of a promoter (H.A. deBoer et al. "Promoters: structure and function", R.L. Rodriguez et al., M.J. Chamberlin ed. (Praeger Co.) 462-481 (1982)): (1) Nucleotide sequence of "-10" region (2) Nucleotide sequence of "-35" region (3) Distance between "-10" and "-35" regions (4) AT content in 5' flanking region of "-35" region (5) Appropriate combination of these factors. Factors (1), (2) and (3) are known to have an important effect on the strength of a promoter. The present inventors presumed that the factor (4) would have an important effect on the strength of a promoter. Some strong Escherichia coli promoters are known to be abundant in adenine (A) and thymine (T) in the 5' flanking region and to contain a part (AT) wherein A and T are linked successively (Z. Humayun et al ., J. Mol. Biol. 112, 265 (1977), G.T. Horn et al ., J. Biol. Chem. 256 , 1998 (1981), G.N. Bennet et al., J. Mol. Biol. 121, 113 (1978), K. Nakamura et al., Cell 18, 1109 (1979)). Further, it is known that the AT content in the 5' flanking region affects the strength of a promoter. G.T. Horn et al. reported that the strength of the P L promoter of λ phage is reduced by the deletion of the 5' flanking region abundant in AT (G.T. Horn et al ., J. Biol. Chem. 256, 2003 (1981) ). Additionally, R.D. Klein et al. reported that the in vitro transcription activity of the lac promoter is enhanced by inserting a double stranded poly(A) poly(T) DNA of about 70 bp upstream of the "-35" region of the lac promoter (J. Biol. Chem. 257, 12954 (1982)). Therefore, it is presumed that the strength of a promoter is increased by insertion of a sequence abundant with AT, into its 5' flanking region. The 5' flanking region of the P L promoter has the following features (see also Table 1). First of all, two regions abundant with AT are contained in the 5' flanking region. According to the conventional numbering wherein the transcription initiation site of P L promoter is indicated by +1 the two regions abundant with AT are -186 to -155 and -101 to -75. G.T. Horn et al. reported that the deletion of both AT-abundant regions resulted in reduction of the strength of the P L promoter but did not change the function of the P L promoter (G.T. Horn et al . J. Biol. Chem. 256, 2003 (1981)). A "-35"-like nucleotide sequence present in the region from -60 to -49 may also have an effect on the strength of the promoter. In the case of the nucleotide sequence of the P L promoter, the sequences of the "-35" region and the "-10" region are very similar to but not identical with the respective consensus sequences. The similarity of the sequences to the consensus sequences is in the same range as in the case of the trp promoter. However, the P L promoter has a stronger transcription activity than the trp promoter. This may be correlated with the difference of the nucleotide sequences in the 5' flanking regions. Therefore, the strength of a promoter wherein the 5' flanking region is replaced with that of the P L promoter may be elevated. In order to replace the 5' flanking region, the method developed by H.A. deBoer et al., that is, the method which comprises recombining the "-35" region containing a 5' flanking region and the "-10" region to construct a new hybrid promoter (Japanese Published Unexamined Patent Application No. 194790/82) is applicable. However, this method does not exclude the possibility to impair the function inherited by a promoter since the recombination site of the "-35" region and the "-10" region is variable. For example, if the method is used to derive a stronger promoter from the very excellent tac promoter by replacing the 5' flanking region with another one, the 5' flanking region and the "-35" region are liable to be simultaneously replaced with other DNA fragments, whereby the "-35" region inherent in the tac promoter is lost. The present inventors have found a process for replacing only the 5' flanking region as described hereinafter, that is, a process for replacing only the 5' flanking region utilizing a restriction site which is present around or upstream from the "-35" region. Summary of the Invention The present invention rebates to a novel promoter which is strengthened in transcription activity. More specifically, this invention relates to a novel promoter which is constructed by replacing a region existing upstream from the "-35" region of an Escherichia coli promoter or an artificially constructed promoter (both referred to as promoter A hereinafter) with the "-35" region of another promoter (referred to as promoter B hereinafter) or a chemically synthesized DNA fragment. Brief Description of the Drawings Fig. 1. illustrates the process for constructing pGHA2. Fig. 2. illustrates the process for constructing pLECl. Fig. 3. illustrates the process for constructing pGHB3. Fig. 4. illustrates the process for constructing pP L T4. Fig. 5. illustrates the process for constructing pTACl0. Fig. 6. illustrates the process for constructing pGC7 and pGA2. Fig. 7. illustrates the process for constructing pGBK3. Fig. 8. illustrates the process for constructing pGTC3. Detailed Description of the Invention The present invention provides a novel promoter wherein the 5' flanking region of a promoter (referred to as promoter A hereinafter) is replaced with the 5' flanking region of another promoter (referred to as promoter B hereinafter) or a chemically synthesized DNA fragment. Examples of promoter A are Escherichia cola -derived promoters such as the promoter of the tryptophan (trp) operon (trp promoter) and the promoter of the lactose (lac) operon (lac promoter), the tac promoter which is a hybrid promoter of the trp promoter and the lac promoter or artificially constructed promoters. As promoter B, a promoter which has a stronger transcription activity than promoter A is preferably used. However, a promoter which has a transcription activity equivalent to or weaker than promoter A is also applicable since the transcription activity may be enhanced by such a replacement. Examples of promoter 3 are Escherichia coli- derived promoters such as the P L promoter of λ phage, the P R promoter of λ phage, the ribosomal RNA promoter (rrn) or the lipoprotein gene promoter. The replacement of the 5' flanking region of promoter A with the 5' flanking region of promoter B or a chemically synthesized DNA fragment is carried out using a restriction site around or upstream from the "-35" region of promoter A or an appropriate restriction site in the "-35" region or the 5' flanking region. If a restriction site in the "-35" region is used it should be selected so as not to convert the nucleotide sequence of the "-35" region by replacement. Further, it is possible to insert the 5' flanking region of promoter B or a chemically synthesized DNA fragment after removing the 5' flanking region of promoter A using a nuclease such as BAL31. For example the following restriction enzymes are suitable to cut out regions from the 5' flanking region of promoter A: In the 5' flanking region of promoter B the respective regions May be cut out by the following restriction enzymes: As the 5' flanking region of promoter B and chemically synthesized DNA fragments, regions and DNA fragments abundant in are preferably used. The present invention is explained in more detail below by referring to the replacement of the 5 flanking region of the trp promotor or the tac promoter with that of the very strong P L promoter. From Table 1 it can be taken that the P L promoter contains a HincII site in the "-35" region. From Tables 2 and 3 it can be taken that the trp promoter and the tac promoter contain a HincII site in their "-35" region at the same position as the HincII site in the P L promoter. Therefore, using these HincII sites, a novels promoter can be constructed wherein a region upstream of the HincII site of the P L promoter is linked to a region downstream from the HincII site of the trp or the tac promoter (see Tables 4 and 5). These novel promoters are designated let (leftward promoter + trp promoter) promoter and lec (leftward promoter + tac promoter) promoter, respectively. Let and lec promoters are constructed using the HincII site in the "-35" region without any chance of the nucleotide sequences in the "-35" region. Therefore, it is possible to enhance the transcription activity without impairing the function of the original trp and tac promoters. In fact, as described below, the let promoter has a transcription activity which is about 10 times stronger than that of the trp promoter and the lec promoter has a transcription activity which is about twice as strong as that of the tac promoter. Both trp promoter and tac promoter contain a part abundant with AT in the 5' flanking region (see Tables 2 and 3). Nevertheless, the transcription activity of the trp and the tac promoter is increased by replacing their 5' flanking regions with that of the P L promoter. This suggests that a specific nucleotide sequence, in addition to the AT content in the 5' flanking region of the P L promoter, contributes to the increase of the transcription activity. Thus, only the 5' flanking region can be replaced using a restriction site around or upstream from the "-35" region. Such a replacement can also be carried out using other methods. For example, in the case of replacing the 5' flanking region of the tac promoter with the respective region of the P L promoter, the desired promoter, like the lec promoter can be constructed by removing the 5' flanking region by digestion with an exonuclease such as BAL31 starting at an appropriate restriction site upstream from the tac promoter, for example, the EcoRI site of pTAC10 as illustrated in Fig. 5, and by subsequently inserting a DNA fragment containing the 5' flanking region of the P L promoter. Further, it is possible to construct a promoter strengthened in transcription activity by inserting the 5' flanking region of another promoter or a chemically synthesized DNA fragment abundant with AT into a restriction site upstream from the "-35" region. Chemical synthesis of DNA fragments is carried out according to the method described in M. Ito et al., Nucleic Acids Res. 10, 1775, (1982). Reaction conditions required for preparing the recombinant plasmid carrying the promoters described above are as follows. The digestion of the DNA with restriction enzymes is usually carried out by reacting 0.1 to 20 µg of DNA with 0.1 - 100 units, Preferably 1 - 3 units of restriction enzyme per 1 µg f DNA in a mixture of 2 - 200-mM preferably 10 - 40 mM Tris-HCl (pH 6.0 - 9.5, preferably pH 7.0 - 8.0), 0 - 200 mM NaCl and 2 - 20 mM, preferably 5- 10 mM MgCl₂ at 20 - 70°C (optimal temperature depends on restriction enzymes used) for 15 minutes to 24 hours. The reaction is usually stopped by heating-to 55 - 75°C for 5- 30 minutes, or alternatively by inactivating the restriction enzyme with a reagent such as phenol or diethylpyrocarbonate. If the purification of the DNA fragment formed by digestion with restriction enzymes is necessary, low-gelling-temperature agarose gel electrophoresis (L. Wieslander, Analytical Biochemistry 98, 305 (1979) ) or polyacrylamide gel electrophoresis (A.M. Maxam et al ., Proc. Natl. Acad. Sci. USA 74 , 560 (1977)) is employed for the purification. The ligation of the DNA fragments is carried out with 0.3 - 10 units of T4DNA ligase in a mixture of 2 - 200mM, preferably 10 - 40 mM Tris-HCl (pH 6.0 - 9.5, preferably 7.0 - 8.0), 2 - 20 mM, preferably 5 - 10 mM MgCl₂, 0.1 - 10 mM, , preferably 0.5 - 2.0 mM ATP and 1 - 50 mM, preferably 5 - 10 mM dithiothreitol at 1 - 37°C, preferably 3 - 20°C for 15 minutes to 72 hours, preferably 2 - 20 hours. If the thus formed recombinant plasmid DNA shall be introduced into Escherichia coli, the plasmid DNA can be introduced by the transformation method of Cohen et al. (Proc. Natl. Acad. Sci. USA 69 , 2110 (1972)). If the recombinant plasmid DNA shall be isolated from Escherichia coli carrying this DNA, the method described in Example 1 or the method of Birnboim et al. (Nucleic Acids Res. 7 , 1513 (1979)) may be employed. The structure of the isolated DNA is analyzed as follows. Plasmid DNA is digested with 1 - 10 types of restriction endonucleases and the resulting fragments are examined by agarose gel electrophoresis or polyacrylamide gel electrophoresis. Further, if necessary, the base sequence of the DNA is determined according to the method of Maxam and Gilbert (Proc. Natl. Acad. Sci. USA 74, 560 (1977)). Recombinant plasmid DNAs can be produced by the method described above. Certain specific embodiments of the present invention are illustrated by the following examples. Example 1 Construction of let promoter and expression of human IFN-γ gene using said promoter: Plasmid pP L T4 carrying P L promoter and constructed according to Reference Example 1, and IFN-γ expressing plasmid pGKA2 constructed according to Reference Example 3 were recombined by the following method to obtain plasmid pGHA2 which expresses human IFN-γ under the control of let promoter wherein the 5' flanking region of the trp promoter is replaced with the respective region of the P L promoter (see Fig. 1). About 10 µg of pP L T4 plasmid DNA (about 4.7 kilo base pairs: referred to as Kb hereinafter) was dissolved in 50 µl of a buffer solution consisting of 10 mM Tris-HCl (pH 7.5), 50 mM NaCl, 7 mM MgCl₂ and 6 mM 2-mercaptoethanol (referred to as "Y-50 buffer solution" hereinafter). 20 units of restriction enzyme PstI (product of Takara Shuzo Co., the restriction enzymes hereinafter are all products of Takara Shuzo Co., unless otherwise specified) were added and the reaction was carried out at 37°C for 1 hour. Subsequently, 4 units of HincII were added and the reaction was continued for 1 hour. In this reaction, the DNA was digested completely with PstI and partially with HincII. After heat treatment at 65°C for 10 minutes, purification was carried out by low-gelling-temperature agarose gel electrophoresis (L. Wieslander, Analytical Biochemistry 98, 305 (1979), hereinafter the method is used in the purification of DNA fragments unless otherwise specified) to obtain a PstI-HincII fragment of about 0.86kb containing a part of the ampicillin (referred to as Ap hereinafter) resistance gene and the 5' flanking region of the P L promoter. Separately, about 10 µg of pGKA2 plasmid (about 5.2 Kb, refer to Reference Example 3) expressing human IFN-γ gene under the control of trp promoter were digested with 20 units of PstI in 50µl of Y-50 buffer solution at 37°C for 1 hour. Then, 4 units of HincII were added and the reaction was continued for 1 hour. In this reaction, the DNA was digested completely with PstI and partially with HincII. After heat treatment at 65°C for 10 minutes, purification was carried out by low-gelling-temperature agarose gel electrophoresis to obtain a HincII-PstI fragment of about 4.2 Kb containing the most part of the trp promoter, the human IFN gene and a part of the Ap resistance gene. About 0.05 µg of the PstI-HincII fragment derived from pP L T4 and about 0.05 µg of the HincII-PstI fragment derived from pGKA2 thus obtained were subjected to ligation reaction with 1 unit of T4 DNA ligase (product of Takara Shuzo Co., the same shall apply hereinafter) at 4°C for 18 hours in 10µl of a buffer solution consisting of 20 mM Tris-HCl (pH 7.6), 10 mM MgCl₂ , 10 mM dithiothreitol and 0.5 mM ATP (referred to as "T4 DNA ligase buffer solution" hereinafter). Escherichia coli HB101 (F hsdR hsdM l pro leu thi rpsL recA, Bolivar et al., Gene 2 , 75 (1977) ) was transformed with the thus obtained recombinant plasmid DNA by the method of Cohen et al. (Proc. Natl. Acad. Sci. USA 69, 2110 (1972), transformation of Escherichia coli is carried out by this method hereinafter) to obtain an Ap resistant strain. Plasmid DNA was isolated from the transformant (named IGHA2) by the following method. - The transformant was inoculated in 8 ml of LG medium (1.0% Bacto-trypton, 0.5% ' yeast extract, 0.5% NaCl, 0.1% ' glucose, pH 7.2) containing 50 µg/ml ampicillin and culturing was carried out at 30°C for 15 - 18 hours. The culture liquor was centrifuged at 10,000-rpm for 5 minutes to harvest cells. The cells were suspended in 400 µl of a buffer solution containing 50 mM Tris-HCl (pH 7.5) and 10 mM EDTA and frozen in dry ice-ethanol. After thawing at 20°C, 40 µl of 2.5 M KCl and 40 µl of 5 mg/ml lysozyme suspension in the buffer solution mentioned above were added and the mixture was allowed to stand in ice for 15 minutes. Freezing and thawing mentioned above were repeated and centrifugation was carried out at 15,000 rpm for 20 minutes to recover a supernatant fluid. The supernatant was extracted with a mixture of phenol and chloroform. Twice as much ethanol (by volume) was added to the extract to precipitate the DNA. The DNA fragment was collected by centrifugation and suspended in 50 - 100 µl of a solution of 10 mM Tris-HCl (pH 7.5) and 1mM EDTA containing 50 µg/ml RNase A (product of Sigma) to prepare partially purified plasmid DNA (this method is used for isolation of plasmid DNAs hereinafter). The structure of the isolated plasmid DNA was analyzed to find out if the plasmid pGHA2 in IGHA2 has the desired structure. In pGHA2, the human IFN-γ gene is ligated upstream from the let promoter constructed by replacing the 5' flanking region of trp promoter with that region of P L promoter. The nucleotide sequence between the Shine-Dalgarno sequence (referred to as SD sequence hereinafter) derived from trpL gene and the ATG initiation codon of IFN-γ gene is the same as that of pGKA2 (AAGGGTATCGATAAGCTTATG) . The nucleotide sequence of the newly constructed let promoter is illustrated in Table 4. As illustrated in Table 4, the let promoter has the form of the portable promoter which is cut out with EcoRI (or XhoI, or BglII) and ClaI (or HindIII). Escherichia coli HB101 carrying recombinant plasmid pGKA2 (IGKA2) and Escherichia coli HB101 carrying pGHA2 (IGHA2) were tested for interferon production by the following method. 10 mℓ of MCG medium. (0.6% Na₂HPO₄, 0.3% KH₂PO₄, 0.5% NaCl, 0.1% NH₄Cl, 0.5% glucose, 0.5% casamino acid, 1 mM MgSO₄, 4 µg/mℓ thiamine hydrochloride, pH 7.2)were inoculated with loopful of the above strains and culturing was carried out at 30°C for 17 hours. The culture broth was centrifuged at 8,000 rpm for 10 minutes to collect cells. The cells were washed with a buffer solution consisting of 30 mM NaCl and 30 mM Tris-HCl (pH 7.5). The washed cells were suspended in 675 µl of PBS buffer solution (0.8 % NaCl, 0.02% KCl, 0.115% Na₂HPO₄, 0.02% KH₂PO₄ (pH 7.4)). 25µl of 0.25 M EDTA and 100 µl of 100 mg/ml lysozyme solution in distilled water were added and the mixture was allowed to stand at 0°C for 30 minutes. Then, 200 µl of 5 M NaCl-5% polyethyleneglycol #1000 were added. Freezing and thawing were repeated three times to disrupt cells. The disrupted cells were centrifuged at 15,000 rpm for 30 minutes to recover a supernatant fluid. The amount of interferon in the supernatant was determined by the method of Armstrong (Appl. Microbiol. 21, 723-725 (1971) ) wherein Sindvis virus was used as a virus and FL cells derived from human amnion cells were used as animal cells. As the result of the measurement of interferon activity, it was found that IGKA2 carrying pGKA2 plasmid which expresses IFN-γ gene under the control of the trp promoter produced about 5 x 10 6 units/ℓ interferon and IGHA2 carrying pGHA2 plasmid which expresses IFN-γ gene under the control of the let promoter produced about 5 x 10⁷ units/ℓ interferon. In view of the fact that plasmids pGKA2 and pGHA2 have the same structure except for the promoter region, it is apparent that the let promoter wherein the 5' flanking region of the trp promoter is replaced with that of the P L promoter has transcription activity which is about 10 times stronger than that of the trp promoter. This also shows that the 5' flanking region of the promoter has a very important effect on the transcription activity. Escherichia coli strains carrying pGKA2 and pGHA2 have been deposited with the Fermentation Research Institute, Agency of Industrial Science and Technology (FERM) as Escherichia coli IGKA2 (FERM P-6798) and IGHA2 (FERM BP-400), respectively. Example 2 Construction of lecI promoter: Plasmid pP L T4 carrying the P L promoter and constructed according to Reference Example 1, and plasmid pTAC10 carrying the tacI promoter and constructed according to Reference Example 2 are recombined by the following method to construct plasmid pLEC1 carrying lecI promoter wherein the 5' flanking region of the tacI promoter was replaced (see Fig. 2). About 5 µg of pTAC10 plasmid carrying the tacI promoter (about 2.6 Kb, refer to Reference Example 2) were digested with 10 units of PstI and 10 units of HincII in 50 µl of Y-50 buffer solution at 37°C for 2 hours. After heat treatment at 65°C for 10 minutes, purification was carried out by low-gelling-temperature agarose gel electrophoresis to obtain a HincII-PstI fragment of about 1.5 Kb containing the most part of the tacI promoter and a part of the Ap resistance gene. About 0.05 µg of the HincII-PstI fragment derived from pTAC10 and obtained as above, and about 0.05 µg or the PstI-HincII fragment derived from pP L T4 and purified in Example 1 were ligated at 4°C for 18 hours with 1 unit of T4 DNA ligase in 10 µl of T4 DNA ligase buffer solution. Escherichia coli JA221 (F⁻hsdR⁻hsdM + trpE5 leu lacY recAl/F' lac I q lac + pro + ) (FERM BP-405) was transformed with the thus obtained recombinant plasmid DNA to obtain an Ap resistant strain. Plasmid DNA was isolated from the transformant (named ILEC1) and the structure thereof was analyzed to determine if the plasmid pLEC1 in ILEC1 has the desired structure. The lecI promoter in pLEC1 is a promoter wherein the 5' flanking region of the tacI promoter was replaced by that region of the P L promoter. The DNA sequence of the lecI promoter is illustrated in Table 5. Since the lecI promoter has a PvuII site five base pairs (referred to as bp hereinafter) downstream from the SD sequence derived from the lacZ gene, insertion of a foreign gene and adjustment of the distance between the SD sequence and ATG initiation codon can readily be made. Escherichia coli strain carrying pLEC1 has been deposited with the FERM a s Escherichia coli ILEC1 (FERM BP-401). Example 3 Expression of human IFN-γ gene by lecI promoter: Plasmid pTAC10 carrying the tacI promoter and constructed according to Reference Example 2, and plasmid pGTC3 for expression of IFN-γ constructed according to Reference Example 4 Were recombined by the following method to obtain plasmid pGHB3 which expresses human IFN-γ under the control of lecI promoter wherein the 5'flanking region of the tacI promoter was replaced with that of P L promoter (see Fig. 3). About 10 µg of pGTC3 plasmid (about 5.15 Kb, see Reference Example 4) which expresses human IFN-γ gene, under the control of the tacI promoter were digested at 37°C for 1 hour with 20 units of PstI in 50 µl of Y-50 buffer solution. Then, 4 units of HincII were added and reaction was continued for 1 hour. In this reaction, the DNA was digested completely with PstI and partially with HincII. After heat treatment at 65°C for 10 minutes, purification was carried out by low-gelling-temperature agarose gel electrophoresis to obtain a HincII-PstI fragment of about 4.2 Kb containing the most part of the tacI promoter, the human IFN gene, the translation termination site of the lipoprotein gene (referred to as lpp terminator hereinafter) and a part of the Ap resistance gene. About 0.05,µg of the thus obtained HincII-PstI fragment derived from pGTC3 and about 0.05 µg of the PstI-HincII fragment derived from pP L T4 and purified in Example 1 were ligated with 1 unit of T4 DNA ligase at 4°C for 18 hours in 10 µℓ of T4 DNA ligase buffer solution. Escherichia coli JA22l was transformed with the thus obtained recombinant plasmid DNA to obtain an Ap resistant strain. Plasmid DNA was isolated from the transformant (named lGHB3) and the structure thereof was analyzed to determine if the plasmid pGHB3 in IGHB3 has the desired structure. In pGHB3, the human IFN-γ gene is inserted downstream from the lecI promoter constructed by replacing the 5' flanking region of the tacI promoter with that region of the P L promoter. The nucleotide sequence between SD sequence derived from lacZ gene and the ATG initiation codon of IFN-γ gene is the same as that of pGTC3 ( AGGA AACAGAGCTT ATG ). Then, Escherichia coli JA221 carrying recombinant plasmid pGTC3 (IGTC3) and Echerichia coli JA221 carrying pGHB3 (IGHB3) were tested for interferon production by the following method. 5 ml of LG medium (1% Bacto-trypton, 0.5% yeast extract, 0.5% NaCl, 0.1% glucose, pH 7.2)were inoculated with the strains and culturing was carried out overnight. 10 ml of MCG medium containing 50 µg/ml tryptophan were inoculated with 0,5ml of the culture and culturing was carried out at 30°C. When OD 550 was about 1.0, 1 mM isopropyl β-D-thiogalactoside (referred to as IPTG hereinafter) was added and culturing was continued for about 4 hours. Cells were harvested and interferon activity in the cell was determined by the method described in Example 1. As the result of the measurement of interferon activity, it was found that IGTC strain carrying pGTC3 plasmid which expresses IFN-γ gene under the control of the tacI promoter produced about 2 x 10⁷ units/ℓ interferon and IGHB3 strain carrying pGHB3 plasmid which expresses IFN-γ gene under the control of the lecI promoter produced about 4 x 10⁷ units/l interferon. In view of the fact that plasmids pGTC3 and pGHB3 have the same structure except for the promoter region, it is apparent that the lecI promoter wherein the 5' flanking region of the tacI promoter was replaced by that of the P L promoter has a transcription activity which is about twice stronger than that of the tacI promoter. This shows that the 5' flanking region of the promoter has an effect on its transcription activity as illustrated in Example 1. Escherichia coli strains carrying pGTC3 and pGHB3 have been deposited with the FERM as Escherichia coli IGTC3 (FERM BP-402) and IGHB3 (FERM BP-403),respectively. Reference Example 1 Construction of plasmid vector pP L T4 carrying the P L -P trp tandem promoter (see Fig. 4): (a) Construction of pP L T2 carrying the P R -P L -P trp tandem promoter: As the source of P L promoter, plasmid pMY12-6 wherein a DNA fragment derived from λ phage is cloned was used (Fig. 4). In pMY12-6 a DNA fragment derived from the λ phage containing the cI gene, the P R promoter and a part of the cII gene and a DNA fragment derived from the λ phage containing the P L promoter are inserted between the PstI site and the BamHI site of plasmid pBR322 (F. Bolivar et al ., Gene 2 , 95 (1977) ). In more detail, according to the numbering of the entire DNA sequence of the λ phage by Sanger et al. (J.Mol. Biol. 162, 729 (1982)), a DNA fragment of 1,350 bp having a PstI end and a HincII end, which is obtained by liking a PstI -BglII fragment from position 37,005 to 38,103 containing the cI gene, the P R promoter and a part of the cII gene to a HaeIII- BglII fragment from position 35,468 to 35,716 containing the P L promoter, is inserted between the PstI site and the BamHI site repaired with DNA polymerase I of pBR322. the cI gene in pMY12-6 is derived from mutant cI857 and therefore shows temperature sensitivity. About 4 µg of pMY12-6 plasmid DNA (about 4.6 Kb) were dissolved in 40 µl of a buffer solution consisting of 10 mM Tris- HCl (pH 7.5), 100 mM NaCl, 7 mM MgCl₂ and 6 mM 2-mercaptoethanol (referred to as "Y-100 buffer solution" hereinafter) and 8 units of BamHI were added. Digestion reaction was carried out at 37°C for 2 hours. After extraction with phenol and chloroform and precipitation with ethanol, the DNA fragment was dissolved in 40 µℓ (total volume) of a buffer solution consisting of 50 mM Tris-HCl (pH 7.6), 7 mM MgCl₂, 6 mM 2-mercaptoethanol, 0.25 mM dATP, 0.25 mM dCTP, 0. 25 mM dGTP and 0.25 mM dTTP (referred to as " DNA polymerase I buffer solution" hereinafter). Then, 6 units of Escherichia coli DNA polymerase I. Klenow fragment (product of Bethesda Research Laboratories, the same shall apply hereinafter) were added. The reaction was carried out at 15°C' for 2 hours to change the 5' -protruding end formed by BamHI digestion to a blunt end. The reaction was stopped by phenol extraction, and after chloroform- extraction and ethanol precipitation, the DNA fragment was dissolved in 40µl (total volume) of Y-50 buffer solution and 8 units of PstI were added. The digestion reaction was carried out at 37°C for 2 hours. After heat treatment at 65°C for 10 minutes purification was carried out by low-gelling-temperature agarose gel electrophoresis to obtain a DNA fragment of about 1.35 Kb containing the cI gene and the promoters P R and P L . Then, about 5 µg of pKYP100 plasmid DNA (T. Nishi et al ., DNA 2, 265-273 (1983)) carrying the trp portable promoter were digested at 37°C for 2 hours with 10 units of XhoI in 40 µl of Y-100 buffer solution. After phenol and chloroform extraction and ethanol precipitation, the DNA fragment was dissolved in 40 µl (total volume) of DNA polymerase I buffer solution and 6 units of Escherichia coli DNA polymerase I , Klenow fragment were added. Reaction was carried out at 15°C for 2 hours to change the 5'-protruding end formed by XhoI digestion to a blunt end. The reaction was stopped by phenol extraction, and after chloroform extraction and ethanol precipitation, the DNA fragment was dissolved in 40 µl (total volume) of Y-5O buffer solution 10 units of PstI were added and the reaction was carried out at 37°C for 2 hours. After heat treatment at 65°C for 10 minutes, the larger DNA fragment containing the trp promoter (about 3.7 Kb) was purified by low-gelling-temperature agarose gel electrophoresis. About 0.1 µl of DNA fragment of about 1.33 Kb derived from pMY12-6 and obtained as described above and the DNA fragment of about 3.7 Kb derived from pKYP100 and obtained as described above were ligated at 4°C for 18 hours with 2 units of T4 DNA ligase in 20 µl of T4 DNA Ligase buffer solution. Escherichia coli MP347 (F - lacZ amY14 trp am8 gal strA (λ bio 252 c I857 ▵HI) (FERM BP-408 was transformed with the thus obtained recombinant plasmid DNA by the method of Cohen et al . to obtain a tetracycline (Tc) resistant strain. Plasmid DNA was isolated from the transformant and its structure was analyzed to determine if the plasmid PP L T2 in IP L T2 has the desired structure. Escherichia coli strains carrying pMY12-6 and pP L T2 have been deposited with the FERM as Escherichia coli IMY12-6 (FERM BP-409) and Escherichia coli I P L T2 (FERM BP-407), respectively. (b) Construction of plasmid vector pP L T4 carrying the P L P trp tandem promoter: The P L -P trp tandem promoter formed by removing the P R promoter and a part of the cII gene from the P R -P L -P trp tandem promoter was inserted in a plasmid carrying an ampicillin (Ap) resistance gene and a Tc resistance gene so as not to lose bath resistances to obtain the plasmid expression vector pP L T4 by the following method. About 5 µg of pP L T2 plasmid DNA were digested at 37°C for 2 hours with 10 units of BglII in 50 µl of Y-100 buffer solution. Then, after phenol and chloroform extraction and ethanol precipitation, the DNA fragment was dissolved in 40 µl (total volume) of DNA polymerase I buffer solution and 6 units of Escherichia coil DNA polymerase I . Klenow, fragment were added. Reaction was carried out at 15°C for 2 hours to charge the 5' protruding end formed by BGlII digestion to a blunt end. The reaction was stopped by phenol extraction, and after chloroform extraction and ethanol precipitation, the DNA fragment was dissolved in 40µl (total volume) of Y-100 buffer solution. 10 units of BamHI were added and the digestion reaction was carried out at 37°00 for 2 hours. After heat treatment at 65°C for 10 minutes, a plasmid DNA fragment of about 0.7 Kb containing P L -P trp tandem promoter was purified by low-gelling-temperature agarose gel electrophoresis. Then, about 5 µg of pKYP100 plasmid DNA were digested at 37°C for 2 hours with 10 units of XhoI in 50 µl of Y-100 buffer solution. After phenol and chloroform extraction and ethanol precipitation, the DNA fragment was dissolved in 40 µl (total volume) of DNA polymerase I buffer solution. 6 units of Escherichia coli DNA polymerase I · Klenow fragment were added and the reaction was carried out at 15°C for 2 hours to change the 5'-protruding end formed by XhoI digestion to a blunt end. The reaction was stopped by phenol extraction, and after chloroform extraction and ethanol precipitation, the DNA fragment was dissolved in 40 µl (total volume) of Y-100 buffer solution. 10 units of BamHI were added and the digestion reaction was carried out at 37°C for 2 hours. After heat treatment at 65°C for 10 minutes, the larger plasmid DNA fragment of about 4.0 Kb was purified by low-gelling-temperature agarose gel electrophoresis. About 0.05 µg of the DNA fragment of about 0.7 Kb derived from pP L T2 and obtained above and 0.1 µg of the DNA fragment of about 4.0 Kb derived from pKYP100 and obtained above were ligated at 4°C for 18 hours with 2 units of T4 DNA ligase in 20 µl of T4 DNA ligase buffer solution. Escherichia coli MP347 was transformed with the recombinant plasmid DNA thus obtained to obtain Ap resistant strains. A Tc resistant strain was selected from the Ap resistant strains and a plasmid DNA was isolated. Its structure was analyzed to determine if the plasmid pP L T4 in IP L T4 has the desired structure. Escherichia coli strain containing pP L T4 has been deposited with the FERM as Escherichia coli IP L T4 (FERM BP-406). Reference Example 2 Construction of the plasmid pTAC10 carrying tacI promoter: (a) Construction of pKYP6 and pKYP30 which carry a DNA fragment containing only the "-35" region of the trp promoter: Plasmid pKYP6 (about 7.35 Kb) carrying a DNA fragment containing only the "-35" region of trp promoter was constructed from plasmid pKYP1 carrying a part of the Escherichia coli trp operon (Japanese Published Unexamined Patent Application No. 213193/81) and plasmid pBR325 according to almost the same method as described in Example 1(b) of the above application. Plasmid pKYP6 has the structure wherein EcoRI TaqI DNA fragment (about 2.6 Kb) containing only the "-35" region of the trp promoter and derived from pKYP1 is inserted between EcoRI site and ClaI site of plasmid pBR325 (see Fig. 5). Then, about 10 µg of pKYP6 plasmid DNA were digested at 37°C for 2 hours with 20 units of PvuII ,and 20 units of HindIII in 50 µl of Y-50 buffer solution. After heat treatment at 65°C for 10 minutes, a DNA fragment (about 240 bp) containing the "-35" region of the trp promoter was purified by low-gelling-temperature agarose gel electrophoresis. Separately, about 5 µg of pBR322 plasmid DNA were dissolved in 50 µl of Y-100 buffer solution. 10 units of EcoRI were added and the digestion reaction was carried out at 37°C for 2 hours. Then, after phenol and chloroform extraction and ethanol precipitation, the DNA fragment was dissolved in 40 µl (total volume) of DNA polymerase I buffer solution. 6 units of Escherichia coli DNA polymerase I · Klenow fragment were added and the reaction was carried out at 15°C for 2 hours to change the 5' -protruding end formed by EcoRI digestion to a blunt end. The reaction was stopped by phenol extraction, and after chloroform extraction and ethanol precipitation, the DNA fragment was dissolved in 50 µl of Y-50 buffer solution. 10 units of HindIII were added and the digestion reaction was carried out at 37°C for 2 hours. After heat treatment at 65°C for 10 minutes, the larger plasmid DNA fragment (about 4.3 Kb) was purified by low-gelling temperature agarose gel electrophoresis. About 0.02 µg of the DNA fragment of about 240 bp derived from pKYP6 and obtained as described above, about 0.1 µg of the DNA fragment of about 4.3 Kb derived from pBR322 and obtained as described above, and 2 pmoles of 5' -phosphorylated EcoRI linker (GGAATTCC: product of Collaborative Research, Inc.) were ligated at 4°C for 18 hours with 2 units of T4 DNA ligase in 20 µl of T4 DNA ligase buffer solution. Escherichia coli K294 (F - hsdR - hsdM + endoI - thi) (ATCC31446, K. Backman et al., Proc. Natl. Acad. Sci. USA 73, 4174 (1976)) was transformed with the thus obtained recombinant plasmid DNA to obtain an Ap resistant strain. Plasmid DNA was isolated from the transformant and its structure was analyzed to determine if the plasmid pKYP30 in strain IKYP30 has the desired structure (see Fig. 5). (b) Construction of plasmid pTAC10 carrying the tacI promoter: As the source of the "-10" region of the lac promoter and the lac operator which are components of the tacI promoter, plasmid pLAC1 was used. Plasmid pLAC1 has the structure wherein and AluI-AluI fragment of 95 bp containing the lacUV5 promoter is inserted between an EcoRI site and a PvuII site of plasmid pBR322 (see Fig. 5). Since religation of an AluI end and a PVuII end creates the nucleotide sequence CAGCTG, the religated region can be recleaved with PvuII. A BamHI site derived from the BamHI linker exists upstream from the lac promoter (see Fig. 5). The lacUV5 promoter is described by W.S. Reznikoff et al . ( "The operon", J.H. Miller and W.S. Reznikoff ed, Cold Spring Harbor Laboratory, New York, 1978, p221). About 10 µg of pLACl plasmid DNA were dissolved in 50 µl of a buffer solution consisting of 10 mM Tris-HCl (pH 7.5), 10 mM NaCl, 7 mM MgCl 2 and 6 mM 2-mercaptoethanol (referred to as "Y-10 buffer solution" hereinafter). 20 units off HpaII and 20 units of PVuII were added and the digestion reaction was carried out at 37°C for 2 hours. After heat treatment at 65°C for 10 minutes, a HpaII-PvuII DNA fragment (55 bp) containing the "-10" region of the lac promoter, the" lac operator and the SD' sequence of lacZ was purified by polyacrylamide gel electrophoresis (A.M. Maxam et al., Proc. Natl. Acad. Sci. USA 74 , 560 (1977)). Then, about 5 µg of plasmid pKYP30 constructed according to Reference Example 2 (a) were dissolved in 50 µl of Y-50 buffer solution. 10 units of ClaI (product of Boehringer Mannheim GmbH, the same shall apply hereinafter). 10 units of PvuII and 15 units of BamHI were added and the digestion reactions was carried out at 37°C for 2 hours. ` After heat treatment at 65°C for 10 minutes, a DNA fragment of about 2.6 Kb containing the "-35" region of the trp promoter and an Ap resistance gene was purified by low-gelling-temperature agarose gel electrophoresis. About 10 ng of the DNA fragment of 55 bp derived from pLACl and obtained above and about 50 ng of the DNA fragment of about 2.6 Kb derived from pKYP30 and obtained as described above were ligated at 4°C for 18 hours with 2 units of T4 DNA ligase in 20 µl of T4 DNA ligase buffer solution. Escherichia coli JA221 was transformed with the recombinant plasmid DNA thus obtained to obtain an Ap resistant strain. Plasmid DNA was isolated from the transformant and its structure was analyzed to determine if the plasmid pTACl0 in ITAC10 has the desired structure (see Fig.5). The Escherichia coli strain containing the recombinant plasmid pTACl0 has been deposited with the FERM as Escherichia coli ITACl0 (FERM BP-404. Reference Example 3 Construction of the recombinant plasmid pGKA2 expressing human IFN-γ: Fig. 6 illustrates the following process of construction of plasmids. (a) Insertion of human IFN-γ DNA into the expression vector pKYP11: In this example, 6 µg of plasmid pIFNγ-G4 isolated from ATCC39123 by the isolation method of plasmids described above was dissolved in 50 µl (total volume) of a solution containing 20 mM Tris-HCl (pH 7.5), 10 mM MgCl 2 , 10 mM dithiothreitol and 50 mM NaCl Then, 12 units each of restriction enzymes PvuII and HindIII were added and the digestion reaction was carried out at 37°C for 4 hours. The reaction solution was heated at 65°C for 7 minutes to inactivate the enzymes and subjected to purification by low-gelling temperature agarose gel electrophoresis to obtain 1.2µg of a DNA fragment containing human IFN-γ DNA of 1.3 Kb. Separately, 4 µg of pKYPll were dissolved in 40 µl (total volume) of a solution containing 20 mM Tris-HCl (pH 7.5), 10 mM MgCl 2, 10 mM dithiothreitol and 50 mM NaCl. 3 units of BamHI were added and the 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 µM 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 µl) were added. Fill-in reaction was carried out at 15°C for 1 hour and the reaction solution was heated at 68°C for 15 minutes to inactivate the DNA polymerase I. 10 units of HindIII were added and digestion reaction was carried out at 37°C for 3 hours, followed by heating at 65°C for 5 minutes to inactivate HindIII. The obtained digestion reaction solution of the Plasmid pKYPll was subjected to purification by low-gelling-temperature agarose gel electrophoresis to obtain about 2.5 µg of a DNA fragment of about 4.7 kb containing P trp . Then, C.5 µg of the DNA fragment of 1.3 Kb containing human IFN-γ DNA and 1.0 µg of the DNA fragment of about 4.7 Kb containing P trp , which was obtained from the plasmid pKYPll, were dissolved in 20 µl of a solution containing 20 mM Tris-HCl (pH 7.5), 6 mM MgCl₂, 5 mM dithiothreitol and 500 µm ATP, and 4 units of T4 DNA ligase (product of New England Biolabs) were added. The ligation reaction was carried out at 4°C for 18 hours, and Escherichia coli HBl0l was transformed with the obtained recombinant plasmid mixture by conventional techniques to obtain an Ap R colony. A plasmid, pGC7 (illustrated in Fig.6) was separated from the culture broth of the colony. The structure of pGC7 was confirmed by digestion with HindIII, BamHI, HpaI, SalI, EcoRI and ClaI and agarose gel electrophoresis. Escherichia coli strain containing pGC7 has been deposited with the FERM as Escherichia coli IGC7 (FERM P-6815, FERM BP-497). (b) Construction of the recombinant plasmid pGKA2: In this example, 6 µg of pGC7 DNA obtained in Reference Example 3 (a) were dissolved in 50 µl (total volume) of a solution containing 20 mM Tris-HCl (pH 7.5), 10 mM MgCl₂, 10 mM dithiothreitol and 10 mM NaCl, and 12 units of BstNI (product of New England Biolabs) was added. the reaction was carried out at 60°C for 3 hours. After heating at 65°C for 5 minutes to inactivate BstNI, 150 mM NaCl and 8 units of SalI were added and the 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 SalI and subjected to purification by low-gelling-temperature agarose gel electrophoresis to obtain about 0.8 µg of a DNA fragment of about 1,125 bp containing the most part of the human IFN-γ DNA. Separately, 3 µg of pKYP10 were dissolved in 40 µl (total volume) of a solution containing 20 mM Tris-HCl (pH 7.5), 10 mM MgCl₂, 10 mM dithiothreitol and 100 mM NaCl. 6 units each of HindIII and SalI were added and the digestion reaction was carried out at 37°C for 3 hours. The reaction solution was heated at 65°C for 5 minutes to inactivate HindIII and SalI and subjected to purification by low-gelling-temperature agarose gel electrophoresis to obtain about 1.8 µg of a DNA fragment of about 4.1 Kb containing P trp . 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 the SD-sequence downstream from P trp and ATG to a suitable length of 6 - 18 bp. Therefore, the following DNA linker was synthesized. An 18-mer and a 15-mer single chain DNA was synthesized by a conventional triester method (R. Crea et al ., Proc. Natl. Acad. Sci. USA 75 , 5765 (1978)). Then of each of the 18-mer and 15-mer DNAs 2 µg were dissolved in 20 µl (total volume) 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 GmbH) were added and phosphorylation reaction was carried out at 37°C for 60 minutes. Then, 2 µg 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 µg of the BstNI - SalI fragment of 1,125 bp obtained as described above and derived from pGC7 and 1.0 µg of the DNA fragment of 4.1 Kb obtained by digestion of the expression vector pKYP10 with HindIII and SalI were dissolved in 25 µl (total volume) of a solution containing 20 mM Tris-HCl (pH 7.5), 6 mM MgCl₂, 5 mM dithiothreitol and 500 µM ATP. About 0.1 µg of the DNA linker mentioned above was added to the mixture, followed by addition of 6 units of T4 DNA ligase. The 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 R colony. A plasmid, pGKA2 (illustrated in Fig. 6), was isolated from the culture broth of the colony. The structure of pGKA2 was confirmed by digestion with EcoRI, ClaI, HindIII, BstNI and SalI and agarose gel electrophoresis. It was confirmed by the method of Maxam and Gilbert (Proc. Natl. Acad. Sci. USA 74 , 560 (1977)) that the base sequence from the SD- sequence (AAGG) to the initiation codon (ATG) in the plasmid pGKA2 is " AAGG GTATCGATAAGCTT ATG ". The human IFN-γ DNA in pGKA2 is different from known DNAs in that the DNA has an RsaI site and the ninth amino acid of the human IFN-γ polypeptide encoded by the DNA is glutamine (Gln). Further, the synthesized DNA used above is different from the one used by P.W. Gray et al . having the following structure: in the underlined parts. Thus, pGKA2 has a restriction site for BstNI, CCAGG, in the DNA region coding for human IFN-γ and this feature also distinguishes pGKA2 from known plasmids. Furthermore, the length and structure of the sequence 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 pGKA2 is apparently different from that in the known recombinant plasmid pIFN-γ trp48 (P.W. Gray et al .). The Escherichia coli strain containing pGKA2 has been deposited with the FERM as Escherichia coli IGKA2 (FERM P-6798, FERM BP-496). Reference Example 4 Construction of the recombinant plasmid pGTC3 expressing human IFN-γ under the control of tac I promoter: As the first step of the construction of the recombinant plasmid the transcription termination site of the Escherichia coli lipoprotein (lpp) gene (referred to as lpp terminator hereinafter) was introduced into the IFN-γ expressing plasmid pGKA2 according to the following processes (a), (b), (c) and (d) (see Fig. 7). (a) Construction of pGBDl: 2 µg of plasmid pIFNγ-G4 (about 3.6 Kb) were dissolved in 20 µl of Y-50 buffer solution and 6 units of PvuII were added. The digestion reaction was carried out at 37°C for 2 hours and stopped by heat treatment at 65°C for 10 minutes. 0.1 µg of the digest were subjected to a ligation reaction in the presence of 5 pmoles of 5' - phosphorylated Bam HI linker (5'-pCCGGATCCGG-3'), product of Collaborative Research Inc.) at 4°C for 18 hours with 2 units of T4 DNA ligase in 20 µl of T4 DNA ligase buffer solution. Escherichia coli HB101 was transformed using the recombinant plasmid DNA thus obtained to obtain an Ap resistant colony. Plasmid DNA was isolated from the transformant. The DNA was digested with restriction enzymes such as BamHI and its structure was analyzed to determine if the recombinant plasmid pGBD1 wherein BamHI linker was inserted at PvuII site of PIFNγ-G4 was obtained. (b) Construction of pKYP14: The construction of the recombinant plasmid pKYP14 used as the source of 1pp terminator is described below. 5 µg of plasmid pKYP10 carrying trp promoter (Japanese Published Unexamined Patent Application No. 110600/83) were dissolved in 40 µl of Y-100 buffer solution. 10 units of BamHI were added and the digestion reaction was carried out at 37°C for 2 hours. Then, 1 µl of Y-100 buffer solution, 2.5 µl of γ M NaCl, 5.5 µl of distilled water and 20 units of SalI were added and the reaction was carried out at 37°C for 2 hours. After heat treatment at 65°C for 10 minutes, the larger plasmid DNA fragment (about 4.9 Kb) was purified by low-gelling-temperature agarose gel electrophoresis. Separately, 5 µg of plasmid pIN-II-Al carrying 1pp terminator (K. Nakamura et al ., The EMBO Journal 1, 771 (1982) ) which is the same as pKEN045 in Japanese Published Unexamined Patent Application No. 140800/82, were digested with BamHI and SalI by the same method as described above. The thus formed HindIII-SalI fragment of about 0.95 Kb containing the 1pp terminator was purified. About 0.1 µg of the DNA fragment derived from pKYP10 and obtained as described above and about 0.05 µg of the DNA fragment derived from pIN-II-Al and obtained as described above were ligated at 4°C for 18 hours with 1 unit of T4 DNA ligase in 20 µl of T4 DNA ligase buffer solution. Escherichia coli HB101 was transformed using the thus obtained recombinant plasmid DNA and plasmid DNA was isolated from the transformant. Its structure was analyzed to determine if the 1pp terminator is inserted downstream from plasmid pKYP14 in IKYP14. (c) Construction of pGBJ2: The insertion of the 1pp terminator downstream from IFN-γ DNA by recombining recombinant plasmids pGBD1 and pKYP14 obtained in (a) and (b) as described above was carried out in the following manner. 5 µg of plasmid pGBD1 (about 3.6 Kb) were dissolved in 30 µl of a buffer solution consisting of 10 mM Tris-HCl (pH 7.5), 7 mM MgCl₂ and 6 mM 2-mercaptoethanol (referred to as "Y-O buffer solution" hereinafter). 10 units of ClaI were added and the digestion reaction was carried out at 37°C for 2 hours. After heat treatment at 65°C for 10 minutes and cooling in ice, 2µl of 10-fold concentrated Y-O buffer solution, 5 µl of 1 M NaCl, 12 µl of distilled water and 2.0 unit of BamHI were added. The digestion reaction was carried out at 37°C for 2 hours. In this reaction, the plasmid DNA was partially digested with BamHI. The thus formed ClaI-BamHI DNA fragment (about 1.3 Kb) containing IFN-γ DNA was purified. Separately, 5 µg of plasmid pKYP14 (about 5.8 Kb) containing the 1pp terminator were digested with 10 units of ClaI and 20 units of BamHI in 50 µl of Y-50 buffer solution for 2 hours and the larger plasmid DNA fragment of about 5.0 Kb containing the 1pp terminator was purified. About 0.1 µg of the DNA fragment derived from pKYP14 and obtained as described above and about 0.05 µg of the DNA fragment derived from pGBD1 and obtained as described above were ligated at 4°C for 18 hours with 1 unit of T4 DNA ligase in 20 µl of T4 DNA ligase buffer solution. Escherichia coli HB101 was transformed using the thus obtained recombinant plasmid. Plasmid DNA was isolated from the transformant and its structure was analyzed to determine if in the plasmid pGBJ2 in strain IGBJ2 the 1pp terminator is inserted downstream from IFN-γ DNA. (d) Construction of pGBK3: The recombinant plasmid pGBJ2 obtained in (c) and the IFN-γ expressing plasmid pGKA2 (see Reference Example 3) were recombined by the following method to construct plasmid pGBK3 in which the 1pp terminator is inserted downstream from IFN-γ DNA. About 5 µg of plasmid pGKA2 (about 5.2 Kb) were dissolved in 30 µl of Y-50 buffer solution. 10 units or more of PstI were added and the digestion reaction was carried out at 37°C for 2 hours. After heat treatment at 65°C for 10 minutes and cooling in ice, 2 µl of 10-fold concentrated Y-150 buffer solution (100 mM Tris-HCl (pH 7.5), 1.5 M NaCl, 70 mM MgCl₂ and 60 mM 2-mercaptoethanol), 3 µl of 1 M NaCl, 14 µl of distilled water and 10 units of NcoI (product of New England Biolabs, the same shall apply hereinafter) were added and the digestion reaction was carried out at 37°C for 2 hours. After heat treatment at 65°C for 10 minutes, a plasmid DNA of about 1.85 Kb containing IFN-γ DNA was purified. About 5 µg of recombinant plasmid pGBJ2 (about 6.4 Kb) obtained as described above were treated by the same method as in the case of pGKA2 and the thus formed PstI-NcoI plasmid DNA fragment of about 4.7 Kb was purified. About 0.1 µg of the thus obtained DNA fragment derived from pGKA2 and about ).1 µg of the thus obtained DNA fragment derived from pGBJ2 were ligated at 4°C for 18 hours with 1 unit of T4 DNA ligase in 20 µl of T4 DNA ligase buffer solution. Escherichia coli HB101 was transformed with the thus obtained recombinant plasmid and plasmid DNA was isolated and purified. Its structure was analyzed to determine if the plasmid pGBK3 in IGBK3 has the desired structure. (e) Construction of pGED13: The plasmid pGED13 wherein a region downstream from the 1pp terminator of pGBK3 was removed was constructed as described below. The resulting recombinant plasmid pGTC3 expresses human IFN-γ under the control of the tacI promoter from pGBK3 obtained in (d) (see Fig. 8). 5 µg of pGBK3 plasmid DNA were dissolved in 50 µl of y_150 buffer solution. 10 units of MluI and 15 units of SalI were added and the digestion reaction was carried out at 37°C for 2 hours. Then, after phenol and chloroform extraction and ethanol precipitation, the DNA fragment was dissolved in 40 µl (total volume) of DNA polymerase I buffer solution. 6 units of Escherichia coli DNA polymerase I · Klenow fragment were added and reaction was carried out at 15°C for 2 hours. After heat treatment at 65°C for 10 minutes, the larger plasmid DNA fragment (about 5.1 Kb) was purified by low-gelling-temperature agarose gel electrophoresis. The thus obtained DNA fragment of about 5.1 Kb derived from pGBK3 was subjected to ligation reaction at 4°C for 18 hours with 1 unit of T4 DNA ligase in 20 µl of T4 DNA ligase buffer solution. Escherichia coli K294 was transformed with the thus obtained recombinant plasmid DNA to obtain an Ap resistant strain. Plasmid DNA was isolated from the transformant and its structure was analyzed to determine if the plasmid pGED13 in IGED13 has the desired structure, i.e. if a region of about 650 bp (between MluI site and SalI site) downstream from the 1pp terminator of pGBK3 was removed and since MluI site and SalI site were repaired with DNA polymerase and religated, if the religated region can be cleaved with MluI and SalI as illustrated by the following base sequence: (f) Construction of pGTC3: 5 µg of pGED13 plasmid DNA obtained above were dissolved in 50 µl of Y-50 buffer solution. 10 units of HindIII were added and the digestion reaction was carried out at 37°C for 2 hours. Then, after phenol and chloroform extraction and ethanol precipitation, the DNA fragment was dissolved in 40 µl (total volume) of DNA polymerase I buffer solution. 6 units of Escherichia coli DNA polymerase I · Klenow fragment were added and the reaction was carried out at 15°C for 2 hours. After phenol and chloroform extraction and ethanol precipitation, the DNA was dissolved in 50 µl (total volume) of Y-50 buffer solution. 10 units of PstI were added and the reaction was carried out at 37°C for 2 hours. After heat treatment at 65°C for 10 minutes, the larger plasmid DNA fragment (about 4.0 Kb) was purified by low-gelling-temperature agarose gel electrophoresis. Then, about 5 µg of pTAC10 carrying the tacI promoter and constructed according to Reference Example 2 were dissolved in 50 µl of Y-50 buffer solution. 10 units of PvuII and 10 units of PstI were added and the digestion reaction was carried out at 37°C for 2 hours. After heat treatment at 65°C for 10 minutes, a DNA fragment of about 1.05 Kb containing the tacI promoter was purified using low-gelling-temperature agarose gel electrophoresis. About 0.1 µg of the thus obtained DNA fragment of about 4.0 Kb derived from pGED13 and about 0.1 µg of the thus obtained DNA fragment of about 1.05 Kb derived from pTAC10 were ligated at 4°C for 18 hours with 1 unit of T4 DNA ligase in 20µl of T4 DNA ligase buffer solution. Escherichia coli JA 221 was transformed with the thus obtained recombinant plasmid DNA to obtain an Ap resistant strain. Plasmid DNA was isolated from the transformant and its structure was analyzed to determine if in the plasmid pGTC3 in strain IGTC3 the IFN-γ gene is inserted downstream from the tacI promoter. Then, in order to examine the nucleotide sequence formed by the ligation of a PvuII end of pTAC10 and a repaired HindIII end of pGED13, the DNA sequence downstream from the HincII site in the tacI promoter of pGTC3 was determined by the method of Maxam and Gilbert (Proc. Natl. Acad. Sci. USA, 74 , 560 (1977)). As the result, the base sequence of the linked region between the SD sequence derived from the lacZ gene and the ATG initiation codon of the IFN-γ gene was determined as follows: The Escherichia coli strain containing the recombinant plasmid pGTC3 has been deposited with the FERM as Escherichia coli IGTC3 (FERM BP-402).

Claims: A promoter wherein a 5' flanking region located upstream of the "-35" region of the trp promoter or the tac promoter is replaced by the 5' flanking region located upstream of the "-35" region of the λ phage P L promoter using a restriction site in the "-35" region of said trp promoter or said tac promoter. A recombinant plasmid which is replicable and contains a foreign gene the expression of which is controlled by a promoter according to claim 1. A microorganism containing the recombinant plasmid according to claim 2. The microorganism according to claim 3 which is Escherichia coli IGHA2 (FERM BP-400), Escherichia col i IGHB3 (FERM BP-403) or Escherichia coli ILEC1 (FERM BP-401).

Inventors: ITOH, SEIGA, NISHI, TATSUNARI, SAITO, AKIKO
Applicants: KYOWA HAKKO KOGYO CO., LTD
Application year: 1984
Main classification: C12N15
IPC codes: C12N1, C07K14, C12R1, C12N15, C07H21