HUMAN PROTEIN S, A PLASMA PROTEIN REGULATOR OF HEMOSTASIS

Abstract: The present invention comprises novel DNA compounds which encode human protein S activity. The human protein S cDNA sequence consists of a coding region for a 676 amino acid precursor; the coding region encodes a 41 amino acid lead­ er peptide, 635 amino acids corresponding to the mature pro­ tein, and a stop codon. Eukaryotic expression vectors have been constructed which comprise the novel protein S activity-­ encoding DNA and drive expression of protein S when trans­ formed into an appropriate host cell.

Description: Thrombin formation, the conversion of pro-thrombin to thrombin, is regulated by a series of reactions, known as the coagulation cascade, that are catalyzed by serine proteases. These proteases depend upon a number of cofactor proteins, such as thrombomodulin, factors Va and VIIIa, and protein S, for maximal activity. Protein S is an important component in the recently discovered protein C-protein S-thrombomodulin system of major importance in the down-regulation of coagulation and intravascular thrombosis. This particular vitamin K-dependent plasma protein is required as a cofactor for optimal activated protein C (APC)-mediated inactivation of Factor Va on phospholipid vesicles and the platelet surface. Protein S is a plasma protein which depends on vitamin K for its biosynthesis. The human protein possesses an apparent M r of 69-85 kilodaltons (Kd) and like other vitamin K-dependent proteins for biological function, it requires extensive post-translational modifications, including the conversion of eleven glutamic acid residues clustered towards the amino-terminus into gamma(γ)-carboxyglutamic acid (Gla), the conversion of three aspartic acid residues (tentatively assigned herein to amino acid residues 95, 135, and 182) into beta-hydroxyaspartic acid, glycosylation (8% weight) and disulfide bond formation. The proposed function of the gamma-carboxyglutamic acid residues is to bind calcium which in turn facilitates the attachment of the molecule to phospholipid bilayer membranes; the function of the beta-hydroxyaspartic acid is unknown. Upon sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) under reducing conditions, a heavy chain of 75 Kd and a light chain of 16 Kd emerges. Upon incubation with thrombin, an 8 Kd fragment is cleaved from the molecule resulting in loss of activity. To define the role of protein S, a brief outline of this anticoagulant system is provided. Protein C, like protein S, depends on vitamin K for its biosynthesis and undergoes the Glu→Gla and the Asp→beta-hydroxyaspartic acid post-translational modifications. Protein C, a normal plasma protein, circulates as a serine protease zymogen. The physiological activator of protein C is thrombin complexed with an endothelial cell membrane glycoprotein, thrombomodulin. Free thrombin is a major coagulant protein; it converts fibrinogen to fibrin, activates platelets and the major cofactors in the clotting cascade, factors Va and VIIIa, thereby providing an important positive feedback loop potently amplifying the coagulation response. In contrast, free thrombin is a slow and ineffective activator of protein C. When complexed with thrombomodulin, thrombin strikingly changes its spectrum of enzymatic activities. Thrombin in complex with thrombomodulin no longer converts fibrinogen to fibrin, activates platelets, or activates clotting factors Va and VIIIa. Instead, thrombo-modulin-thrombin becomes a highly efficient activator of protein C. Activated protein C has two points of attack. It proteolytically degrades and inactivates the activated forms of cofactors Va and VIIIa, whereas the precursor forms of cofactors Va and VIIIa are very poor substrates for activated protein C. Protein S is an important cofactor for activated protein C. In the absence of protein S, activated protein C only minimally degrades and inactivates cofactors Va and VIIIa. These complex reactions first established in vitro have important clinical corollaries. Homozygous protein C deficiency results in development of purpura fulminans, a lethal form of disseminated intravascular coagulation occurring in infancy or early childhood. The number of case reports of heterozygous protein C and especially protein S deficiency associated with deep vein thrombosis and recurrent pulmonary embolism are rapidly mounting and a preliminary estimate suggests that 10% of all cases of recurrent deep vein thrombosis-pulmonary embolism represent heterozygous protein S deficiency. Moreover, recent evidence strongly suggests that acquired protein S deficiency may be a common disorder. Protein S exists in the circulation in two forms: as free protein S and in a one-to-one complex with C4b-binding protein. C4b-binding protein possesses a M r of 570 Kd and serves an important function in down-regulating the complement system in the fluid phase and on cell surfaces. Protein S complexed with the C4b-binding protein has no known biological activity. In pregnancy and immediately post-partum, a shift from free to bound forms of protein S occurs with a sharp decrease in functional protein S activity. In the nephrotic syndrome, the proportion of protein S complexed with C4b-binding protein is increased and the levels of free protein S are significantly reduced. In addition, for reasons not completely clear at this time, the specific activity of free protein S in the nephrotic syndrome is substantially reduced. In systemic lupus erythematosus (SLE) in which complement activation is present, a shift from free to bound protein S is again observed. Each of these disease states are associated with a high incidence of thromboembolism. The shift from free to bound protein S then may represent a control point at which inflammation or other physiological changes can directly influence the hemostatic balance. A less drastic but still significant decrease in free, biologically active protein S has also been observed in disseminated intravascular coagulation and liver disease. Although the binding of protein S to the C4b-binding protein abolishes protein S activity, it does not appear that the complex loses C4b-binding protein activity. However, it is tempting to speculate that protein S with its gamma-carboxyglutamic acid residues designed to anchor this protein to phospholipid bilayer cell membranes may serve to transport the C4b-binding protein to membrane sites of complement down regulation. Protein S has been isolated from both human and bovine plasma. The bovine protein S consists of a single polypeptide chain with a reported molecular weight of 64 Kd. In contrast, the apparent molecular weight of human protein S is reported to be 69-85 Kd. While methods are available for the isolation of protein S from plasma, until the present invention, very little was known about the primary or secondary structure of protein S. Notwithstanding the lack of information concerning protein S, the biological and potential therapeutic importance of protein S can be deduced from clinical observations. Presently available information indicates that hereditary protein S deficiency may be a common disorder. Protein S-deficient patients are predisposed to venous thrombotic disease at a relatively young age. Heterozygotes are at risk for superficial thrombophlebitis, deep vein thrombosis and pulmonary embolism. Given the severe consequences of protein S deficiency, it would be extremely advantageous to clone and express the gene for human protein S for use as a valuable adjunct in antithrombotic therapy. Definitions ApR - the ampicillin-resistant phenotype or gene conferring same. ep - a DNA segment comprising the SV40 early promoter of the T-antigen (A) gene, the T-antigen binding sites, and the SV40 origin of replication. Expression Vector - any recombinant DNA cloning vector into which a promoter has been incorporated and positioned to drive transcription of a desired gene. Human Protein S - A precursor polypeptide including intermediate forms such as pro-protein S, des-carboxy protein S, non-glycosylated protein S, and the mature protein, wherein all forms of the protein demonstrate protein S activity. HmR - the hygromycin-resistant phenotype or gene conferring same. IVS - a DNA encoding an intron, also called an intervening sequence. NeoR - the neomycin-resistant phenotype or gene conferring same. Ori - a plasmid origin of replication. pA - a DNA sequence encoding a polyadenylation signal. Promoter - a DNA sequence that directs transcription of DNA into RNA. Protein S activity - any property of human protein S responsible for biological function or anti-human protein S antibody-binding activity. Replicon - A DNA sequence that controls and allows for autonomous replication of a plasmid or other vector. Structural gene - any DNA sequence that encodes a functional polypeptide, inclusive of translational start and stop signals. TcR - the tetracycline-resistant phenotype or gene conferring same. Translational Activating Sequence - any DNA sequence, inclusive of that encoding a ribosome binding site and translational start codon, such as 5'-ATG-3', that provides for the translation of a mRNA transcript into a peptide or polypeptide. The present invention relates to novel DNA compounds and recombinant DNA expression vectors that encode a polypeptide precursor for human protein S activity. The vectors allow expression of the novel DNA compounds in eukaryotic host cells. The invention also relates to host cells transformed with these vectors. Human liver cDNA coding for protein S has been cloned and sequenced. The cDNA sequence consists of a coding region for a 676 amino acid precursor, flanked by 5'- and 3'-noncoding segments. The coding region encodes a 41 amino acid leader peptide, 635 amino acids corresponding to the mature protein and a stop codon. Accordingly, it is an object of the present invention to provide the DNA sequence coding for human protein S and its precursor. It is a further object of the present invention to provide the primary structure of the protein possessing human protein S activity. Additionally, it is an object of the present invention to provide a plasmid comprising a gene encoding human protein S precursor. Brief Description of the Drawings Figure 1 is a restriction site and function map of plasmid pShd. Figure 2 is a restriction site and function map of plasmid pHHS-IIa. The Pst I restriction site noted in parenthesis is not reconstituted. Figure 3 is a restriction site and function map of plasmid pBKE1. Figure 4 is a restriction site and function map of plasmid pBkneo1. Figure 5 is a restriction site and function map of plasmid pSV2cat. Figure 6 is a restriction site and function map of plasmid pLPcat. Figure 7 is a restriction site and function map of plasmid pBLcat. Figure 8 is a flow chart illustrating the construction of plasmid pL133. Figure 9 is a restriction site and function map of plasmid pLPC. Figure 10 is a restriction site and function map of plasmid pLPC4. Figure 11 is a restriction site and function map of plasmid pSV2hyg. Figure 12 is a restriction site and function map of plasmid pLPChyg1. Figure 13 is a restriction site and function map of plasmid pLPChd1. Figure 14 is a restriction site and function map of plasmid phd. The present invention relates to recombinant human protein S produced by means of a double-stranded deoxyribonucleic acid that encodes a polypeptide with human protein S activity. The entire amino acid sequence of human protein S precursor, as well as the coding strand of DNA encoding a polypeptide with human protein S activity is presented below. The amino acid sequence of the protein S precursor is based upon the cDNA sequence. The precursor schematically consists of seven distinct domains and one unknown region. These regions are grouped by approximate amino acid (aa) boundries as follows: leader peptide (aa-41 to -1); a γ-carboxyglutamate (Gla) segment (aa 1-37); a linker region (aa 38-73); four epidermal growth factor domains (aa 74-121, 122-165, 166-207, 208-248); and an unknown region (aa 249-635). The numbering of amino acid residues herein is based upon the assignment of +1 to the amino terminal residue of the mature protein (residue number 42 in the precursor protein sequence shown above). The invention further provides recombinant DNA plasmids comprising a gene encoding human protein S and micro-organisms or cell lines transformed by these plasmids. The DNA compounds of the present invention are derived from a single cDNA clone prepared from human liver mRNA that encodes the entire gene, including both 5' and 3' noncoding sequences, for human protein S precursor Initially, a cDNA library was prepared in a lambda (λ) gtll expression vector ( lac 5 nin 5 cI857 S 100) according to the procedure described by Young and Davis, 1983, Proc. Natl. Acad. Sci. USA 80 :1194-1198. The recombinant human liver cDNA library constructed in λgt11 was obtained from Clontech Laboratories, Inc., 922 Industrial Avenue, Palo Alto, California 94303. This library was screened using conventional methods with polyclonal antibodies raised in a goat against human protein S. Approximately 2 x 10⁶ individual recombinants were screened in the form of phage plaques on a lawn of Escherichia coli Y1090. E . coli Y1090 is available from the ATCC under the accession number 37197. To protect against the possibility that the fusion protein might be toxic to the host, plaque formation was initiated without expression from the lac Z gene promoter by incubating the plates at 42°C. After the number of infected cells surrounding the plaques was large, lac Z-directed gene expression was induced by the addition of isopropylthio-β-galactoside (IPTG). This was accomplished by placing an IPTG-impregnated nitrocellulose filter disk over the lawn. After a period of incubation, the nitrocellulose filters with bound protein were washed, treated with primary antibody, then biotinylated secondary antibody, followed by avidin-peroxidase conjugate. Positive colonies were identified by a color reaction when exposed to hydrogen peroxide. The identified positives were picked and re-tested at a density of about 5000 plaques per plate. Several of the positive plaques were picked and re-screened at a density of about 400 plaques per plate. Using isolated plaques from the latter screen, large amounts of purified phage DNA were isolated. The initial step taken to map the cDNA insert in the phage clones was to determine the size(s) of the EcoRI fragment(s). In the construction of the library, the cDNA fragments were ligated to artificial Eco RI linkers and inserted into a unique Eco RI site in the λgt11 molecule. Digesting a recombinant phage DNA molecule with Eco RI would generate the two lambda "arms" (19.6 and 24.1 Kb); any other fragments produced thereby correspond to the inserted DNA. (If the DNA sequence of the insert contained no internal Eco RI site then only one Eco RI fragment would be generated. Correspondingly, one or more internal Eco RI sites would result in two or more additional Eco RI fragments). Accordingly, the purified phage DNA was digested with Eco RI and separated by electrophoresis on either a 3.5% polyacrylamide gel or a 1.0% agarose gel. One of the largest clones, designated 1-1, contained two Eco RI fragments of 1.8 Kb and 0.8 Kb. The Eco RI fragments isolated from this clone were subsequently subcloned into plasmid pBR322 and used to transform E . coli RR1 cells. After transformation and plasmid identification, the plasmid DNA was amplified and purified in preparation for DNA sequencing. The subcloned DNA fragments from clones designated pLHS-21 and pLHS-22 were sequenced according to the teaching of Maxam and Gilbert, 1980, Methods in Enzymology 61 :497. Localization of the particular DNA sequences within the Eco RI-generated restriction fragments was accomplished by Southern transfer analysis. Two independent, mixed probes, described below in Table 1, were used for the hybridization procedure. These probes were chemically synthesized either by using a Systec 1450A DNA Synthesizer (Systec Inc., 3816 Chandler Drive, Minneapolis, MN 55421) or an ABS 380A DNA Synthesizer (Applied Biosystems, Inc., 850 Lincoln Centre Drive, Foster City, CA 94404). Many DNA synthesizing instruments are known in the art and can be used to make the fragments. In addition, the fragments can also be conventionally prepared in substantial accordance with the procedures of Itakura et al ., 1977, Science 198 :1056 and Crea et al ., 1978, Proc. Natl. Acad. Sci. USA 75 :5765. Probe 80 corresponds to amino acid residues 83-90 of one of the EGF domains of the bovine amino acid sequence presented by J. Stenflo (Xth International Congress on Thrombosis and Haemostasis, San Diego, California, July, 1985). Probe 81 was also based upon the bovine sequence and corresponds to the carboxy terminal amino acid residues 628-634. These two probes hybridized strongly to the ∼1.8 Kb Eco RI subcloned fragment. Once the sequencing data had been obtained, it became apparent that the complete coding sequence of protein S, specifically the 5' end of the molecule, was not represented in the clones generated from the λgt11 library. Therefore, a second library was utilized to generate the missing sequence. Based upon the sequenced DNA, two probes, designated 21 and 22 in Table 2 below, were derived from identified λgt11 clones. Probe 22 corresponds to a 3' non-translated region of the molecule and was used to locate 3' regions of cDNA. In contrast, probe 21, corresponding to a region of the 5' end of the molecule, was used to locate the 5' coding portion of the molecule. These probes were radioactively labelled and used to probe the cDNA library. After hybridization, several positives were identified using restriction enzyme mapping, Southern hybridization and DNA sequencing. One clone, designated pHHS-IIa contains sequences corresponding to the complete protein S precursor as well as 5' and 3' non-coding segments. Plasmid pHHS-IIa contains ∼3.3 Kb of cDNA corresponding to messenger RNA (mRNA) which is significantly larger than the ∼2.5 Kb size reported by Stenflo, 1985. Northern analysis of both bovine and human liver mRNA with human cDNA probes shows that the RNA species differ in a manner consistent with the sizes of the cDNAs. Plasmid pHHS-IIa can be conventionally isolated from E . coli K12RRI/pHHS-IIa, a strain deposited with and made part of the permanent stock culture collection of the Northern Regional Research Laboratory (NRRL), Peoria, Illinois. A culture of E . coli K12 RR1/pHHS-IIa can be obtained from the NRRL under the accession number B-18071. A restriction site and function map of plasmid pHHS-IIa is presented in Figure 2 of the accompanying drawings. Alternatively, the specific DNA sequences of the present invention can be chemically synthesized by using a DNA synthesizer as previously described. Despite the rather large size of the protein S gene, double-stranded DNA segments containing more than 1000 deoxynucleotides are generated quite easily today with the aid of these "gene machines" (see Caruthers, M. H., 1985, Science 230 :281). A variety of recombinant DNA expression vectors comprising the protein S activity-encoding DNA can be constructed. Many mammalian host cells possess the necessary cellular machinery for the recognition and proper processing of the leader peptide present on the amino-terminus of human protein S. Some mammalian host cells also provide the post-translational modifications, such as glycosylation, γ-carboxylation, and β-hydroxylation, as are observed in human protein S present in blood plasma. A wide variety of vectors exist for the transformation of eukaryotic host cells, and the specific vectors exemplified below are in no way intended to limit the scope of the present invention. Two embodiments of the present invention utilize pSV2-type vectors as starting material in the construction of eukaryotic expression vectors. The pSV2-type vectors comprise segments of the SV40 genome that constitute a defined eukaryotic transcription unit-promoter (ep), intervening sequence (IVS), and polyadenylation (pA) site. In the absence of SV40 T-antigen, the plasmid pSV2-type vectors transform mammalian and other eukaryotic host cells by integrating into the host cell chromosomal DNA. A variety of plasmid pSV2-type vectors are known in the art (see Eukaryotic Viral Vectors , edited by Gluzman, published by Cold Spring Harbor Laboratories, Cold Spring Harbor, New York, 1982), such as plasmids pSV2-gpt, pSV2-neo, pSV2-dhfr, and pSV2-β-globin, in which the SV40 promoter drives transcription of an inserted gene. These vectors are available either from the American Type Culture Collection (ATCC) in Rockville, Maryland or from the aforementioned NRRL. Amino acid residues -41 to -18 at the amino-terminus of human protein S may act as a signal peptide to direct secretion of protein S from the liver into the bloodstream. These residues are not present in mature protein S. Residues -17 to -1 of human protein S precursor, which likely comprise the pro-peptide of human protein S, are also removed during the processing and activation of the protein and are believed responsible for the correct folding and modification of the molecule. Although not specifically exemplified herein, the present invention also comprises protein S derivatives such as "pro-protein S". The present DNA compounds are readily modified to delete that portion. encoding amino and residues -41 to -18 of human protein S precursor for expression of the resulting derivative. Skilled artisans will recognize that the present invention is not limited to the expression of a particular protein S derivation in eukaryotic hosts. As a general rule, prokaryotes do not efficiently process eukaryotic signal peptides; therefore, it would be somewhat inefficient to express the signal peptide-encoding portion of the human protein S precursor gene in prokaryotes. Although not specifically exemplified herein, the present invention also comprises the fusion of a prokaryotic signal peptide-encoding DNA to the protein S activity-encoding DNA of the present invention for expression and secretion of protein S activity in prokaryotes. Useful starting materials for the preparation of the expression vectors of the present invention include expression vectorsin which the BK virus enhancer (Enh) is used in the presence of an immediate-early gene product of a large DNA virus to increase transcription of a recombinant gene in eukaryotic host cells. Thus, such vectors are useful to express the protein S encoding gene of the present invention. The construction of these vectors is described in detail in Examples 8-17. A brief over-view of their construction immediately follows. The BK virus (ATCC VR-837) can be purchased or readily isolated in large quantities as described in Example 8. Alternatively, it is also convenient to clone the BK viral DNA onto a plasmid cloning vector and use the recombinant vector as a source of BK viral DNA sequences. Consequently, BK viral DNA was digested with restriction enzyme Eco RI, which, due to the presence of only one Eco RI site on the BK genome, produced linear BK DNA. Plasmid pUC8 (available from Bethesda Research Laboratories (BRL), P.O. Box 6009, Gaithersburg, MD 20877) was likewise digested and linearized with restriction enzyme Eco RI, and the Eco RI-cut plasmid pUC8 DNA was ligated to the Eco RI-cut BK viral DNA to form plasmids pBKE1 and pBKE2, which differ only with respect to the orientation of the BK viral DNA. A restriction site and function map of plasmid pBKE1 is presented in Figure 3 of the accompanying drawings. The construction of plasmids pBKE1 and pBKE2 is described in Example 9. The BK viral genome has also been combined with a portion of plasmid pdBPV-MMTneo to construct plasmids pBkneo1 and pBkneo2. Plasmid pdBPV-MMTneo, about 15 Kb in size and available from the ATCC under the accession number ATCC 37224, comprises the replicon and β-lactamase gene from plasmid pBR322, the mouse metallothionein promoter (MMTpro) positioned to drive expression of a structural gene that encodes a neomycin resistance-conferring enzyme, and about 8 Kb of bovine papilloma virus (BPV) DNA. Plasmid pdBPV-MMTneo can be digested with restriction enzyme Bam HI to generate two fragments: the ∼8 Kb fragment that comprises the BPV DNA and an ∼7 Kb fragment that comprises the other sequences described above. BK virus has only one Bam HI restriction site, and plasmids pBKneo1 and pBKneo2 were constructed by ligating the ∼7 Kb Bam HI restriction fragment of plasmid pdBPV-MMTneo to Bam HI-linearized BK virus DNA. The construction of plasmids pBKneo1 and pBKneo2, which differ only with respect to the orientation of the BK virus DNA, is described in Example 10, and a restriction site and function map of plasmid pBKneo1 is presented in Figure 4 of the accompanying drawings. An additional vector, useful as starting material in the construction of the present expression vectors, is designated plasmid pBLcat. This plasmid comprises the BK enhancer sequence in tandem with the human adenovirus-type-2 late promoter (Ad2LP) positioned to drive expression of the chloramphenicol acetyltransferase enzyme (CAT). Plasmid pSV2cat serves as a convenient source of the CAT gene and can be obtained from the ATCC under the accession number ATCC 37155. A restriction site and function map of plasmid pSV2cat is presented in Figure 5 of the accompanying drawings. Human adenovirus-type-2 DNA is commercially available and can also be obtained from the ATCC under the accession number ATCC VR-2. Briefly, plasmid pBLcat was constructed by ligating the ∼0.32 Kb late-promoter-containing Acc I- Pvu II restriction fragment of human adenovirus-type-2 DNA to blunt-ended Bcl I linkers that attached only to the Pvu II end of the Acc I- Pvu II restriction fragment. The resulting fragment was then ligated to the ∼4.51 Kb Acc I- Stu I restriction fragment of plasmid pSV2cat to yield an intermediate plasmid pLPcat, for which a restriction site and function map is presented in Figure 6 of the accompanying drawings. The desired plasmid pBLcat was constructed from plasmid pLPcat by ligating the origin of replication and enhancer-containing, ∼1.28 Kb Acc I- Pvu II restriction fragment of BK virus DNA to the ∼4.81 Kb Acc I- Stu I restriction fragment of plasmid pLPcat. A restriction site and function map of the resultant plasmid pBLcat is presented in Figure 7 of the accompanying drawings. The construction of plasmid pBLcat is further described in Example 11. Plasmid pBLcat is a convenient source of a BK enhancer-adenovirus late promoter "cassette" which is an ∼870 bp Hin dIII restriction fragment that can be conveniently inserted into a eukaryotic expression vector to increase expression of a product encoded by that vector. For example, the BK enhancer-adenovirus late promoter cassette was used to improve expression of human protein C by ligating the cassette into plasmid pL133. A restriction site and function map of plasmid pL133 is presented in Figure 8 of the accompanying drawings. Plasmid pL133 is also a convenient expression vector to use for the expression of protein S. This plasmid can be digested with restriction enzyme Bcl I (to delete the fragment containing the protein C gene) and treated with Klenow to generate a linear, blunt-ended fragment. The entire protein S gene, contained on an ∼2.7 Kb Fnu DII- Eco RV restriction fragment can then be ligated to the Klenow-treated Bcl I vector fragment to generate a protein S expression vector. Plasmid pL133, the construction of which is given in Example 12, is also used as an intermediate vector to construct additional expression vectors. Thus, the plasmid was digested with restriction enzyme Hin dIII and then ligated to the ∼0.87 Kb Hin dIII restriction fragment of plasmid pBLcat to yield plasmid pLPC. A restriction site and function map of plasmid pLPC is presented in Figure 9 of the accompanying drawings, and the construction of plasmid pLPC is further described in Example 13. Plasmid pLPC, like plasmid pL133, comprises the enhancer, early and late promoters, T-antigen-binding sites, and origin of replication of SV40. These elements are closely situated together on the SV40 DNA and are difficult to delineate. The binding of T antigen to the T-antigen-binding sites, which is necessary for SV40 replication, is known to enhance transcription from the SV40 late promoter and surprisingly has a similar effect on the BK early and late promoters. Because the high level of T-antigen-driven replication of a plasmid that comprises the SV40 origin of replication is generally lethal to the host cell, neither plasmid pLPC nor plasmid pL133 are stably maintained as episomal (extrachromosomal) elements in the presence of SV40 T antigen, but rather, the two plasmids must integrate into the chromosomal DNA of the host cell to be stably maintained. To construct a derivative of plasmid pLPC that can exist as a stably-maintained element in a transformed eukaryotic cell, the entire BK genome, as an Eco RI-linerarized restriction fragment, was inserted into the single Eco RI restriction site of plasmid pLPC. This insertion produced two plasmids, designated pLPC4 and pLPC5, that differ only with respect to the orientation of the BK Eco RI fragment. A restriction site and function map of plasmid pLPC4 is presented in Figure 10 of the accompanying drawings, and the construction of plasmids pLPC4 and pLPC5 is further described in Example 14. Episomal maintenance of a recombinant DNA expression vector is not always preferred over integration into the host cell chromosome. However, due to the absence of a selectable marker that functions in eukaryotic cells, the identification of stable, eukaryotic transformants of plasmid pLPC is difficult, unless plasmid pLPC is cotransformed with another plasmid that does comprise a selectable marker. Consequently, plasmid pLPC has been modified to produce derivative plasmids that are selectable in eukaryotic host cells. This was done by ligating plasmid pLPC to a portion of plasmid pSV2hyg, a plasmid that comprises a hygromycin resistance-conferring gene. A restriction site and function map of plasmid pSV2hyg, which can be obtained from the NRRL, under the accession number NRRL B-18039, is presented in Figure 11 of the accompanying drawings. Plasmid pSV2hyg was digested with restriction enzyme Bam HI, and the ∼2.5 Kb Bam HI restriction fragment, which comprises the entire hygromycin resistance-conferring gene, was isolated, treated with Klenow enzyme (the large fragment produced upon subtilisin cleavage of E . coli DNA polymerase I), and then ligated to the Klenow-treated, ∼5.82 Kb Nde I- Stu I restriction fragment of plasmid pLPC to yield plasmids pLPChyg1 and pLPChyg2. Plasmids pLPChyg1 and pLPChyg2 differ only with respect to the orientation of the hygromycin resistance-conferring fragment. A restriction site and function map of plasmid pLPChyg1 is presented in Figure 12 of the accompanying drawings, and the construction protocol for plasmids pLPChygl and pSPChyg2 is described in Example 15. Plasmid pLPChyg1 was modified to introduce a dihydrofolate reductase (dhfr) gene. The dhfr gene is a selectable marker in dhfr-negative cells and can be used to increase the copy number of a DNA segment by exposing the host cell to increasing levels of methotrexate. The dhfr gene was obtained from plasmid pSV2-dhfr (ATCC 37146). The use of a particular dhfr gene is not critical in the construction of the present vectors. After isolation, the dhfr gene-containing, ∼1.9 Kb Bam HI restriction fragment was treated with Klenow enzyme and inserted into partially- Eco RI-digested plasmid pLPChyg1 to yield plasmids pLPChd1 and pLPChd2. Plasmid pSPChyg1 contains two Eco RI restriction enzyme recognition sites, one in the hygromycin resistance-conferring gene and one in the plasmid pBR322-derived sequences. The fragment comprising the dhfr gene was inserted into the Eco RI site located in the pBR322-derived sequences of plasmid pLPChyg1 to yield plasmids pLPChd1 and pLPChd2. A restriction site and function map of plasmid pLPChd1 is presented in Figure 13 of the accompanying drawings. The construction of plasmids pLPChd1 and pLPChd2, which differ only with respect to the orientation of the dhfr gene-containing DNA segment, is described in Example 16. Plasmid pLPChd1 was modified to form plasmid phd, a plasmid that contains both the BK enhancer-adenovirus late promoter cassette and also the hygromycin resistance-conferring and dhfr genes. To construct plasmid phd, plasmid pLPChd1 was prepared from dam - E . coli host cells, digested with restriction enzyme Bcl I, and recircularized, thus deleting the human protein C-encoding DNA. Plasmid phd contains a single Bcl I restriction enzyme recognition site, which is conveniently positioned for the insertion of any sequence desired to be expressed from the BK enhancer-adenovirus late promoter of the present invention. A restriction site and function map of plasmid phd is presented in Figure 14 of the accompanying drawings, and the construction protocol for plasmid phd is described in Example 17. Ultimately, plasmid pShd of the present invention was constructed by ligating the ∼2.7 Kb protein S-containing Fnu DII- Eco RV restriction fragment from plasmid pHHS-IIa to Bcl I-digested Klenow-treated plasmid phd. The resulting expression vector utilizes the BK enhancer-adenovirus late promoter cassette to drive expression of human protein S. An alternative embodiment of the present invention can be constructed as taught above by simply replacing the protein C gene, bounded by Bcl I restriction sites in plasmid pL133 (which are then treated with Klenow), with the ∼2.7 Kb Fnu DII- Eco RV restriction fragment isolated from plasmid pHHS-IIa. The resulting expression vector utilizes the SV40 early promoter to drive expression of human protein S. Both of these protein S expression vectors are useful for the production of human protein S. It is anticipated that protein S can become a valuable adjunct in antithrombotic therapy in several areas. The most obvious is heterozygous protein S deficiency which, as mentioned previously, may involve a sizable number of patients with recurrent deep-vein thromhosis-pulmonary embolism. It is envisioned that protein S be given as intravenous infusions to such patients during acute thrombotic episodes. It is also anticipated that protein S will be useful in the treatment of acquired protein S deficiency so far identified during pregnancy and SLE and in the nephrotic syndrome. It is not unreasonable to anticipate that the list of disease states associated with acquired protein S deficiency may grow to cover many acute and chronic inflammatory conditions as well as autoimmune diseases and cancer. The dose required can be established with certainty only in preclinical and clinical trials and the following calculations should be considered only tentative. The normal level of total protein S in plasma is 30 µg/ml and the normal level of free protein S is 10-15 µg/ml. If one desires to elevate circulating levels of protein S in a patient by 5-10 µg/ml, this would require 30-60 mg administered intravenously provided the volume of distribution of protein S is similar to that of factor IX. The biological half-life of protein S has been established to be 40-48 hours in man. Therefore, infusions every 36-48 hours probably would suffice to cover a patient during the acute phases of his illness. The possibility exists that protein S might serve a useful function in helping to attach the C4b-binding protein to membrane surfaces at sites where complement activation is occurring. Should this hypothesis prove valid, the therapeutic role of protein S could be expanded to include numerous disease states in which complement activation is an important pathogenetic factor including a wide array of autoimmune and infectious diseases. The following examples further illustrate the invention disclosed herein. The examples describe the procedures used for the isolation and identification of genetic material encoding human protein S, as well as procedures available for the chemical synthesis of the gene encoding human protein S activity. Procedures used in the construction of expression vectors are also disclosed. Explanations of the procedures are provided where appropriate. Example 1 Screening and Identification of λgt11 Phage Expressing a Protein that Reacts with a Polyclonal Antibody to Human Protein S The particular λgt11 library used in the present invention is commercially available from Clontech Laboratories, Inc., 922 Industrial Ave., Palo Alto, California 94303. The λgt11 library was generated from human liver cDNA and had a complexity of 5 x 10⁵ plaques. This library was diluted and about 200,000 phage were plated on each of ten 150 mm dishes containing TY agar (10 g tryptone, 10 g NaCl, 5 g yeast extract and 15 g agar per liter). The procedure used for the screening, described below, was essentially that of the supplier. Immediately after the phage were plated the dishes were incubated at 42°C for 3½ hours. Each plate was overlayed with a nitrocellulose filter saturated with 10 mM IPTG and shifted to 37°C for about 16 hours. The plates were chilled at 4°C for at least 15 minutes before the filters were marked with India ink and transferred to a wash buffer, TBST (50 mM Tris-HCl pH=7.9, 150 mM NaCl, 0.05% Tween-20). The filters were washed in 200 ml of this buffer three times at five minutes/wash. All washes and reactions were done at room temperature. To reduce non-specific binding of the antibody to the nitrocellulose, the filters were then treated with 20% fetal calf serum in TBST for 30 minutes and washed as before. The initial antibody reaction utilized a polyclonal antibody raised in a goat against human Protein S. These antibodies can be isolated using any of a number of conventional techniques included in Methods in Enzymology 104 : 381-387. After one hour of incubation with the primary antibody, the filters were again washed and then treated with a biotinylated secondary antibody (Vector Laboratories, Inc., Burlingame, CA 94010) for 30 minutes. The filters were washed and transferred to TBST containing the avidin-conjugated horseradish peroxidase complex for 30 minutes. For the final wash only TBS is used--the Tween-20 is eliminated. The peroxidase substrate solution was prepared by mixing 3 mg/ml of 4-chloronapthol in methanol with TBS plus 0.01 M imidazole. Three percent hydrogen peroxide was added to 1/250 volume and the solution was immediately added to the filters. The color reaction ("positive" plaques turn purple) was complete within 30 minutes. Once positive plaques had been identified, the corresponding region of the original plate was removed and added to sterile lambda dilution buffer (10 mM Tris-HCl pH=7.5, 10 mM MgSO₄) and stored at 4°C with a few drops of chloroform. Later these phage were plated at a density of about 5000 plaques per 100 mm dish and screened by the same procedure. Positive plaques were subjected to a third round of screening at a density of about 100 plaques per 100 mm dish and isolated plaques were collected and stored as before. Example 2 Mapping and Subcloning of the cDNA Region of the Purified Phage Large amounts of purified phage DNA were isolated using the plate lysate technique (Davis, Botstein and Roth, 1980, Advanced Bacterial Genetics , Cold Spring Harbor Laboratories) as follows. Ten 150 mm dishes were each plated with E . coli infected with about 10⁶ plaque-purified phage. Nearly confluent lysis was achieved after four hours at 42°C. At this point, the plates were chilled for one hour at 4°C, flooded with 10 ml of 0°C lambda dilution buffer, and stored at 4°C overnight. The buffer was carefully removed the next morning and treated with a few drops of chloroform to lyse any remaining cells. Phage particles were removed from the supernatant by centrifugation at 20,000 rpm for 3 hours at 18°C and the pellet was resuspended in 1 ml of lambda dilution buffer. The phage particles were further purified using cesium chloride gradients: the 1 ml phage sample was layered over a step gradient of 1 ml of Solution I (5 M CsCl, 10 mM MgSO₄, 0.1 mM Na₂EDTA, 10 mM Tris, pH=8.0); and 3 ml of Solution II (3 M CsCl, 10 mM MgSO₄, 0.1 mM Na₂EDTA). After 60 minutes at 30,000 rpm (18°C) a faint blue band, corresponding to the phage particles, could be seen at the interphase. Using a syringe and needle, 0.5 ml of the solution was removed at the interphase. At this point, a second gradient could be performed if desired. To release phage DNA from the protein coat, an equal volume of deionized formamide was mixed with each sample and left at room temperature for more than 30 minutes. The solution was diluted with 0.5 ml of water and the DNA precipitated with two volumes of room temperature ethanol. The DNA was collected by centrifugation for 10 minutes at 10,000 rpm; the pellet was rinsed with 5 ml of 68% ethanol (-20°C), dried and resuspended in 500 µl of TE (10 mM Tris-HCl, pH=8.0 and 1 mm EDTA). A total of 200-1000 µg of total phage DNA can be recovered. Phage DNA from each of six positive clones was tested to determine the size(s) of the Eco RI fragments(s) generated from the cDNA insert. About 50 µg of purified DNA were digested in a volume of 200 µl containing 20 µl of 10X Eco RI buffer (100 mM Tris-HCl pH=7.5, 10 mM MgCl₂, 50 mM NaCl) and 50 units of Eco RI for 90 minutes at 37°C. All enzyme units referred to herein, unless otherwise indicated, refer to the unit definitions of New England Biolabs, 32 Tozer Road, Beverly, MA 01915, although the actual source of the enzymes may have been different. The samples were precipitated with ethanol and then separated by electrophoresis on either a 3.5% polyacrylamide gel (29:1, acrylamide:bis-acrylamide) or a 1.0% agarose gel along with appropriate commercially available size markers. The DNA was visualized using ethidium bromide and the size of each band calculated based upon its migration in the gel. Similar digestions were done using Xmn I, Sst I and Kpn I to verify the size of the insert and the orientation of the fragments. One of the largest clones, designated 1-1, contained Eco RI fragments of 1.8 and 0.8 Kb thereby giving a total insert size of 2.6 Kb. The initial subclones were generated from Eco RI digests of clone 1-1. About 50 µg of phage DNA were digested with Eco RI as described above for subsequent ligation to about 100 ng of Eco RI-digested, dephosphorylated pBR322. The ligation was done in a total volume of 20 µl of 1X ligase buffer (50 mM Tris-HCl, pH=7.8, 10 mM MgCl₂, 20 mM DDT, 1 mM ATP) with 400 units of ligase at 15°C overnight. E . coli RR1 cells, commercially available from Bethesda Research Laboratories, Inc. Gaithersburg MD 20877, were used for transformation according to the protocol provided by Bethesda Research Laboratories and the transformed cells were selected on TY plates containing 50 µg/ml of ampicillin. The plates were incubated at 37°C overnight. Plasmid DNA was isolated from 12 randomly selected clones and digested with Eco RI to determine the size of the subcloned fragments. The predicted 1.8 and 0.8 Kb fragments were individually subcloned into pBR322 and the resulting plasmids designated pLHS-22 and pLHS-21 respectively. Large amounts of plasmid DNA were purified in preparation for DNA sequencing using chloramphenicol amplification in minimal media followed by alkaline lysis as described by Maniatis, Fritsch, and Sambrook, 1982, Molecular Cloning , Cold Spring Harbor Laboratories. Example 3 Fifty ug in 60 µl of H₂O of the plasmid pLHS-22 were mixed with 20 µl of 10X Eco RI reaction buffer and 120 µl of water. This mixture was digested with 50 units of Eco RI at 37°C until the digestion was complete. The Eco RI digested DNA was separated by electrophoresis on a 3.5% polyacrylamide gel until the ∼1.8 Kb band was separated from the other digestion products. The gel was then stained in a dilute solution of ethidium bromide so that the bands could be visualized with ultraviolet light. The region of the gel containing the ∼1.8 Kb Eco RI restriction fragment was cut from the gel, placed in a test tube, and broken into small fragments. One ml of extraction buffer (500 mM NH₄OAc, 10 mM MgOAc, 1 mM EDTA, and 1% SDS) was added to the tube containing the fragment. The tube was incubated at 37°C overnight. The acrylamide was removed by centrifugation and the supernatant was transferred to a new tube. The acrylamide was washed once with 200 µl of extraction buffer, centrifuged again, the supernatants combined and passed through a plug of glass wool to remove any remaining contaminants. The DNA was precipitated with two volumes of ethanol, mixed well and kept in a dry ice-ethanol bath for 10 to 30 minutes. The DNA was recovered by centrifugation. About 15 µg of the ∼1.8 Kb Eco RI restriction fragment were recovered by this procedure. The purified fragment was resuspended in 10 µl of TE buffer and stored at 4°C. Example 4 Sequencing Strategy of the cDNA Coding for Human Protein S The DNA sequence of the cDNA coding for human Protein S was determined in substantial accordance with the teaching of the Maxam and Gilbert protocol (Methods in Enzymology , 1980). Example 5 Southern Analysis of Protein S Subclones Plasmid DNA was prepared from several of the protein S Eco RI fragments subcloned into pBR322 (described in Example 3) including the 1.8 and 0.8 Kb fragments from phage 1-1. The DNAs were digested with Eco RI as taught in Example 2 and separated by electrophoresis on a 1.0% agarose gel. The conditions for preparation of the gel, the actual transfer and the hybridization were in substantial accordance with the teaching of Smith and Summers, 1980, Anal Biochem , 109 :123-129. Two independent, mixed probes, described in Table 1, were used for the hybridization. As previously discussed, the first probe, #80, was derived from bovine amino acid seguence presented by J. Stenflo, 1985. This probe corresponds to amino acids #83-90 in one of the EGF domains of the bovine molecule. Probe 81, also based upon the bovine sequence, corresponds to the carboxy terminal amino acids #628-634. The 1.8 Kb Eco RI fragment from phage 1-1 hybridized strongly to both of these probes. Example 6 Five mls of L-broth (10 g peptone, 10 g NaCl, and 5 g yeast extract) were inoculated with a culture of E . coli RR1/pHHS-IIa (NRRL B-18071) and incubated in an air shaker at 37°C for about 16 hours. A small amount of this culture was streaked on a L-broth agar plate containing 15 µg/ml of tetracycline and grown at 37°C for about 16 hours. An isolated colony was inoculated into 5 ml of L-broth containing 15 µg/ml of tetracycline and grown, with shaking, for about 16 hours at 37°C. This culture was then used to inoculate one liter of L-broth containing 12 µg/ml tetracycline and incubated in an air-shaker at 37°C until the optical density (O.D.) at 590 nm was ∼0.6 absorbance unit, at which time 250 mg of chloramphenicol were added to the culture. The incubation was continued for about 16 hours; the chloramphenicol addition inhibits protein synthesis, and thus inhibits further cell division, but allows plasmid replication to continue. B. Isolation of Plasmid pHHS-IIa The culture prepared in Example 6A was centrifuged in a Sorvall GSA rotor (DuPont Co., Instrument Products, Biomedical Division, Newtown, CN 06470) at 6000 rpm for 5 minutes at 4°C. The resulting supernatant was discarded. The cell pellet was frozen at -20°C for a minimum of 2 hours and then thawed. The thawed cell pellet was resuspended in 6.25 ml of a 25% sucrose/50 mM Tris-HCl, pH=8 solution. After adding and mixing: 1.5 ml of a 10 mg/ml lysozyme solution; 1.25 ml of 0.5 M EDTA, pH=8.0; the solution was incubated on ice for 10 minutes. Ten ml of lysing solution (0.1% Triton X-100, 0.125 M EDTA, pH=8, 50 mM Tris, pH=8.) were added to the lysozyme-treated cells, mixed, and the resulting solution incubated on ice for another 10 minutes. The cellular debris was removed from the solution by centrifugation at 19,000 rpm for 30 minutes in an SS34 rotor (Sorvall). The solution volume was adjusted to 30 ml with TE and then 28.9 g of CsCl and 3.75 ml of a 10 mg/ml ethidium bromide solution were added and the solution decanted into a Vti50 ultracentrifuge tube (Beckman, Lincolnwood, IL 60646). After sealing the tube, the solution was centrifuged in a Vti50 rotor at 49,000 rpm for ∼16 hours. The resulting plasmid band, visualized with ultraviolet light, was isolated. The ethidium bromide was extracted with TE-saturated isobutanol, and the solution diluted with 3 volumes of H₂O. One-fortieth volume of 2.0 M NaOAc, pH=5 and two volumes of ethanol were then added to the solution, followed by incubation overnight at -20°C. The plasmid DNA was pelleted by centrifuging the solution in an SS34 rotor (Sorvall) for 30 minutes at 10,000 rpm. The DNA was resuspended in 5 ml of 0.3 M NaOAc. To this, 10 ml of ethanol were added and the solution was incubated overnight at -20°C. The plasmid DNA was pelleted as taught immediately above. The ∼1 mg of plasmid pHHS-IIa DNA obtained by this procedure was suspended in 1 ml of TE buffer and stored at 4°C. A restriction site and function map of plasmid pHHS-IIa is presented in Figure 2 of the accompanying drawings. Example 7 Probing Human Liver cDNA Library As the phage clone 1-1 lacked DNA sequences at both the 5' and 3' ends of the molecule it was necessary to screen again for clones containing additional sequence. For this step a different human liver cDNA library was utilized. This library, which uses the pBR322 vector, is described elsewhere (R.J. Beckmann, et al ., Nuc. Acid Res. 13 :5233, 1985). Based upon the known DNA sequence, two probes were isolated and designated 21 and 22. The sequence of each is given in Table 2. Probe 21, homologous to a region of the 5' end, consisted of a 110 bp fragment bounded by the recognition sequences for Hin cII and Hin dIII. Probe 22 corresponds to a 3' non-translated region of the molecule and was a 130 bp fragment bounded by the recognition sequences for Hin fI and Eco RI. These probes were radio-actively labelled and used to probe the cDNA library using standard techniques (Maniatis, et al ., 1982). The probes were hybridized and washed at 68°C and all filters were done in duplicate. Several positives were identified by this method. Using restriction enzyme mapping, Southern hybridization and DNA sequencing, one clone, designated pHHS-IIa was identified as containing the complete coding region of the protein S precursor. Example 8 Preparation of BK Virus DNA BK virus is obtained from the American Type Culture Collection under the accession number ATCC VR-837. The virus is delivered in freeze-dried form and resuspended in Hank's balanced salts (Gibco, 3175 Staley Road, Grand Island, NY 14072) to a titer of about 10⁵ plaque-forming units (pfu)/ml. The host of choice for the preparation of BK virus DNA is primary human embryonic kidney (PHEK) cells, which can be obtained from Flow Laboratories, Inc., 7655 Old Springhouse Road, McLean, VA 22101, under cataloque number 0-100 or from M.A. Bioproducts under catalogue number 70-151. About five 75 mm² polystyrene flasks comprising confluent monolayers of about 10⁶ PHEK cells are used to prepare the virus. About 1 ml of BK virus at a titer of 10⁵ pfu/ml is added to each flask, which is then incubated at 37°C for one hour before fresh culture medium (Delbecco's Modified Eagle's Medium, Gibco, supplemented with 10% fetal bovine serum) is added, and the infected cells are incubated at 37°C for 10-14 days or until the full cytopathogenic effect of the virus is noted. This cytopathogenic effect varies from cell line to cell line and from virus to virus but usually consists of cells rounding up, clumping, and sloughing off the culture disk. The virus is released from the cells by three freeze-thaw cycles, and the cellular debris is removed by centrifugation at 5000Xg. The virus in 1 liter of supernatant fluid is precipitated and collected by the addition of 100 g of PEG-6000, incubation of the solution for 24 hours at 4°C, and centrifugation at 5000Xg for 20 minutes. The pellet is dissolved in 0.1X SSC buffer (1XSSC = 0.15 M NaCl; 5 mM EDTA; and 50 mM Tris-HCl, pH=7.8) at 1/100th of the original volume. The virus suspension is layered onto a 15 ml solution of saturated KBr in a tube, which is centrifuged at 75,000Xg for 3 hours. Two bands are evident in the KBr solution after centrifugation. The lower band, which contains the complete virion, is collected and desalted on a Sephadex G-50 column using TE as an elution buffer. Sodium dodecyl sulfate (SDS) is added to the solution of purified virions obtained from the column to a concentration of 1%; pronase is added to a concentration of 100 µg/ml, and the solution is incubated at 37°C for 2 hours. Cesium chloride is then added to the solution to a density of 1.56 g/ml, and ethidium bromide is added to the solution to a final concentration of 100 µg/ml. The solution is centrifuged in a Sorval 865 rotor or similar vertical rotor at 260,000Xg for 24 hours. After centrifugation, the band of virus DNA is isolated and extracted five times with isoamyl alcohol saturated with 100 mM Tris-HCl, pH=7.8. The solution of BK virus DNA is then dialyzed against TE buffer until the 260 nm/280 nm absorbance ratio of the DNA is between 1.75 and 1.90. The DNA is precipitated by adjusting the NaCl concentration to 0.15 M, adding two volumes of ethanol, incubating the solution at -70°C for at least 2 hours, and centrifuging the solution at 12,000Xg for 10 minutes. The resulting pellet of BK virus DNA is suspended in TE buffer at a concentration of 1 mg/ml. Example 9 Construction of Plasmids pBKE1 and pBKE2 About one µg of the BK virus DNA prepared in Example 8 in one µl of TE buffer was dissolved in 2 µl of 10X Eco RI buffer (1.0 M Tris-HCl, pH=7.5; 0.5 M NaCl; 50 mM MgCl₂; and 1 mg/ml BSA) and 15 µl of H₂O. About 2 µl (∼10 units) of restriction enzyme Eco RI were added to the solution of DNA, and the resulting reaction was incubated at 37°C for two hours. About 1 µg of plasmid pUC8 (available from Pharmacia P-L Biochemicals, 800 Centennial Ave., Piscataway, NJ 08854) in 1 µl of TE buffer was digested with Eco RI in substantial accordance with the procedure used to prepare the Eco RI-digested BK virus DNA. The Eco RI-digested plasmid pUC8 DNA was diluted to 100 µl in TE buffer; ∼0.06 units of calf-intestinal alkaline phosphatase were added to the solution, and the resulting reaction was incubated at 37°C for 30 minutes. The solution was adjusted to contain 1X SET (5 mM Tris-HCl, pH=7.8; 5 mM EDTA; and 150 mM NaCl), 0.3M NaOAc, and 0.5% SDS and then incubated at 65°C for 45 minutes. The phosphatase treatment prevents the pUC8 DNA from self ligating. The Eco RI-digested BK virus and plasmid pUC8 DNA were extracted first with buffered phenol and then with chloroform. The DNA was collected by adjusting the NaCl concentration of each DNA solution to 0.25 M, adding two volumes of ethanol, incubating the resulting mixtures in a dry ice-ethanol bath for 5 minutes, and centrifuging to pellet the DNA. The supernatants were discarded, and the DNA pellets were rinsed with 70% ethanol, dried, and resuspended in 10 µl and 30 µl of TE buffer for the BK and plasmid pUC8 samples, respectively. About 3 µl of H₂O and 1 µl of 10X ligase buffer were added to a mixture of 2 µl of the Eco RI-digested BK virus and 1 µl of the Eco RI-digested plasmid pUC8 DNA. One µl (∼1000 units) of T4 DNA ligase were added to the solution of DNA, and the resulting reaction was incubated at 16°C overnight. The ligated DNA constituted the desired plasmids pBKE1 and pBKE2, which differ only with respect to the orientation of the inserted BK virus DNA. A restriction site and function map of plasmid pBKE1 is presented in Figure 3 of the accompanying drawings. A 50 ml culture of E . coli K12 JM103, available from Pharmacia P-L Biochemicals, in L-broth was grown to an optical density at 650 nanometers (O.D.₆₅₀) of approximately 0.4 absorbance units. The culture was chilled on ice for ten minutes, and the cells were collected by centrifugation. The cell pellet was resuspended in 25 ml of cold 100 mM MgCl₂ and incubated on ice for 25 minutes. The cells were once again pelleted by centrifugation, and the pellet was resuspended in 2.5 ml of cold 100 mM CaCl₂ and incubated for 30 minutes on ice. After the incubation, the cells are competent for the uptake of transforming DNA. This procedure is used in the following examples requiring the use of competent cells. Two hundred µl of this cell suspension were mixed with the ligated DNA prepared above and incubated on ice for 30 minutes. At the end of this period, the cells were placed in a water bath at 42°C for 2 minutes and then returned to the ice for an additional 10 minutes. The cells were collected by centrifugation and resuspended in one ml of L broth and incubated at 37°C for 1 hour. Aliquots of the cell mixture were plated on L-agar (L broth with 15 grams of agar per liter) plates containing 100 µg ampicillin/ml, 40 µg X-gal/ml, and 40 µg IPTG/ml. The plates were incubated at 37°C overnight. Colonies that contain a plasmid without an insert, such as E . coli K12 JM103/pUC8, appear blue on these plates. Colonies that contain a plasmid with an insert, such as E . coli K12 JM103/pBKE1, are white. Several white colonies were selected and screened by restriction enzyme analysis of their plasmid DNA for the presence of the ∼5.2 Kb Eco RI restriction fragment of BK virus. Plasmid DNA was obtained from the E . coli K12 JM103/pBKE1 and E . coli K12 JM103/pBKE2 cells in substantial accordance with the procedure for isolating plasmid DNA that is described in the following example, although the procedure is done on a smaller scale, and the CsCl gradient steps are omitted, when the plasmid. DNA is isolated only for restriction enzyme analysis. Example 10 Construction of Plasmids pBKneo1 and pBKneo2 E . coli K12 HB101/pdBPV-MMTneo cells are obtained in lyophil form from the American Type Culture Collection under the accession number ATCC 37224. The lyophilized cells are plated on L-agar plates containing 100 µg/ml ampicillin and incubated at 37°C to obtain single colony isolates. One liter of L broth containing 50 µg/ml ampicillin was inoculated with a colony of E . coli K12 HB101/pdBPV-MMTneo and incubated in an air-shaker at 37°C until the O.D.₅₉₀ was ∼1 absorbance unit, at which time 150 mg of chloramphenicol were added to the culture. The incubation was continued for about 16 hours; the chloramphenicol addition inhibits protein synthesis, and thus inhibits further cell division, but allows plasmid replication to continue. The culture was centrifuged in a Sorvall GSA rotor (DuPont Co., Instrument Products, Biomedical Division, Newtown, CN 06470) at 6000 rpm for 5 minutes at 4°C. The resulting supernatant was discarded, and the cell pellet was washed in 40 ml of TES buffer (10 mM Tris-HCl, pH=7.5; 10 mM NaCl; and 1 mM EDTA) and then repelleted. The supernatant was discarded, and the cell pellet was frozen in a dry ice-ethanol bath and then thawed. The thawed cell pellet was resuspended in 10 ml of a solution of 25% sucrose and 50 mM EDTA. About 1 ml of a 5 mg/ml lysozyme solution; 3 ml of 0.25 M EDTA, pH=8.0; and 100 µl of 10 mg/ml RNAse A were added to the solution, which was then incubated on ice for 15 minutes. Three ml of lysing solution (prepared by mixing 3 ml 10% Triton-X 100; 75 ml 0.25 M EDTA, pH=8.0; 15 ml of 1 M Tris-HCl, pH=8.0; and 7 ml of water) were added to the lysozyme-treated cells, mixed, and the resulting solution incubated on ice for another 15 minutes. The lysed cells were frozen in a dry ice-ethanol bath and then thawed. The cellular debris was removed from the solution by centrifugation at 25,000 rpm for 40 minutes in an SW27 rotor (Beckman, 7360 N. Lincoln Ave., Lincolnwood, IL 60646) and by extraction with buffered phenol. About 30.44 g of CsCl and ∼1 ml of a 5 mg/ml ethidium bromide solution were added to the cell extract and the volume of the solution was adjusted to 40 ml with TES buffer. The solution was decanted into a VTi50 ultra-centrifuge tube (Beckman), which was then sealed and centrifuged in a VTi50 rotor at 42,000 rpm for ∼16 hours. The resulting plasmid band, visualized with ultraviolet light, was isolated and then placed in a Ti75 tube and rotor (Beckman) and centrifuged at 50,000 rpm for 16 hours. Any necessary volume adjustments were made using TES containing 0.761 g/ml CSCl: The plasmid band was again isolated, extracted with salt-saturated isopropanol to remove the ethidium bromide, and diluted 1:3 with TES buffer. Two volumes of ethanol were then added to the solution, which was then incubated overnight at -20°C. The plasmid DNA was pelleted by centrifuging the solution in an SS34 rotor (Sorvall) for 15 minutes at 10,000 rpm. The ∼1 mg of plasmid pdBPV-MMTneo DNA obtained by this procedure was suspended in 1 ml of TE buffer and stored at -20°C. The foregoing plasmid isolation procedure is generally used throughout the following examples when large amounts of very pure plasmid DNA are desired. The procedure can be modified to rapidly obtain a smaller, less pure amount of DNA, such as is needed when screening transformants for the presence of a given plasmid, by using only about 5 ml of cultured cells, lysing the cells in an appropriately scaled-down amount of lysis buffer, and replacing the centrifugation steps with phenol and chloroform extractions. About 5 µg (5 µl) of the plasmid pdBPV-MMTneo DNA prepared above and five µg (5 µl) of the BK virus DNA prepared in Example 8 were each digested at 37°C for 2 hours in a solution containing 2 µl of 10X Bam HI buffer (1.5 M NaCl; 60 mM Tris-HCl, pH=7.9; 60 mM MgCl₂; and 1 mg/ml BSA), 1 µl of restriction enzyme Bam HI, and 7 µl of H₂O. The reaction was stopped by an extraction with an equal volume of phenol, followed by two extractions with chloroform. Each Bam HI-digested DNA was then precipitated, collected by centrifugation, and resuspended in 5 µl of H₂O. About 1 µl of 10X ligase buffer was added to a mixture of Bam HI-digested plasmid pdBPV-MMTneo (1 µl) and Bam HI-digested BK virus DNA (1 µl). After 1 µl (∼1000 units) of T4 DNA ligase and 6 µl of H₂O were added to the mixture of DNA, the resulting reaction was incubated at 16°C overnight. The ligated DNA constituted the desired plasmids pBKneoI and pBKneo2, which differ only with respect to the orientation of the BK virus DNA. A restriction site and function map of plasmid pBKneo1 is presented in Figure 4 of the accompanying drawings. E . coli K12 HB101 cells are available in lyophilized form from the NRRL under the accession number NRRL 5-15626. E . coli K12 HB101 cells were cultured, made competent for transformation, and transformed with the ligated DNA prepared above. The transformed cells were plated on L-agar plates containing 100 µg/ml ampicillin. E . coli K12 HB101/psKneol and E . coli K12/pBKneo2 transformants were identified by their ampicillin-resistant phenotype and by restriction enzyme analysis of their plasmid DNA. Example 11 Construction of Plasmid pBLcat A. Construction of Intermediate Plasmid pLPcat The virion DNA of adenovirus 2 (Ad2) is a double-stranded linear molecule about 35.94 Kb in size. The Ad2 late promoter can be isolated on an ∼0.316 Kb Acc I- Pvu II restriction fragment of the Ad2 genome; this ∼0.32 Kb restriction fragment corresponds to the sequence between nucleotide positions 5755 and 6071 of the Ad2 genome. To isolate the desired ∼0.32 Kb Acc I- Pvu II restriction fragment, Ad2 DNA is first digested with restriction enzyme Bal I, and the ∼2.4 Kb Bal I restriction fragment that comprises the entire sequence of the ∼0.32 Kb Acc I- Pvu II restriction fragment is isolated. Then, the ∼2.4 Kb Bal I restriction fragment is digested with Acc I and Pvu II to obtain the desired fragment. About 50 µg of Ad2 DNA (available from BRL) are dissolved in 80 µl of H₂O and 10 µl of 10X Bal I buffer (100 mM Tris-HCl, pH=7.6; 120 mM MgCl₂; 100 mM DTT; and 1 mg/ml BSA). About 10 µl (∼20 units) of restriction enzyme Bal I are added to the solution of Ad2 DNA, and the resulting reaction is incubated at 37°C for 4 hours. The Bal I-digested DNA is loaded onto an agarose gel and electrophoresed until the restriction fragments are well separated. Visualization of the electrophoresed DNA is accomplished by staining the gel in a dilute solution (0.5 µg/ml) of ethidium bromide and exposing the stained gel to long-wave ultraviolet (UV) light. One method to isolate DNA from agarose is as follows. A small slit is made in the gel in front of the desired fragment, and a small piece of NA-45 DEAE membrane (Schleicher and Schuell, Keene, NH 03431) is placed in each slit. Upon further electrophoresis, the DNA non-covalently binds to the DEAE membrane. After the desired fragment is bound to the DEAE membrane, the membrane is removed and rinsed with low-salt buffer (100 mM KCl; 0.1 mM EDTA; and 20 mM Tris-HCl, pH=8). Next, the membrane is placed in a small tube and immersed in high-salt buffer (1 M NaCl; 0.1 mM EDTA; and 20 mM Tris-HCl, pH=8) and then incubated at 65°C for one hour to remove the DNA from the DEAE paper. After the 65°C incubation, the incubation buffer is collected and the membrane rinsed with high-salt buffer. The high-salt rinse solution is pooled with the high-salt incubation buffer. The volume of the high salt-DNA solution is adjusted so that the NaCl concentration is 0.25 M, and then three volumes of cold, absolute ethanol are added to the solution. The resulting solution is mixed and placed at -70°C for 10-20 minutes. The solution is then centrifuged at 15,000 rpm for 15 minutes. After another precipitation to remove residual salt, the DNA pellet is rinsed with ethanol, dried, resuspended in 20 µl of TE buffer, and constitutes about 3 µg of the desired restriction fragment of Ad2. The purified fragment obtained is dissolved in 10 µl of TE buffer. About 6 µl of H₂O and 2 µl of 10X Acc I buffer (60 mM NaCl; 60 mM Tris-HCl, pH=7.5; 60 mM MgCl₂; 60 mM DTT; and 1 mg/ml BSA) are added to the solution of the ∼2.4 Kb Bal I restriction fragment of Ad2. After the addition of about 2 µl (∼10 units) of restriction enzyme Acc I to the solution of DNA, the reaction is incubated at 37°C for 2 hours. After the Acc I digestion, the DNA is collected by ethanol precipitation and resuspended in 16 µl of H₂O and 2 µl of 10X Pvu II buffer (600 mM NaCl; 60 mM Tris-HCl, pH=7.5; 60 mM MgCl₂; 60 mM DTT; and 1 mg/ml BSA). After the addition of about 2 µl (about 10 units) of restriction enzyme Pvu II to the solution of DNA, the reaction is incubated at 37°C for 2 hours. The Acc I- Pvu II-digested, ∼2.4 Kb Bal I restriction fragment of Ad2 is loaded onto an ∼6% polyacrylamide gel and electrophoresed until the ∼0.32 Kb Acc I- Pvu II restriction fragment that comprises the Ad2 late promoter is separated from the other digestion products. The gel is stained with ethidium bromide and viewed using UV light, and the segment of gel containing the ∼0.32 Kb Acc I- Pvu II restriction fragment is cut from the gel, crushed, and soaked overnight at room temperature in ∼250 µl of extraction buffer. The following morning, the mixture is centrifuged, and the pellet is discarded. The DNA in the supernatant is precipitated with ethanol; about 2 µg of tRNA are added to ensure complete precipitation of the desired fragment. About 0.2 µg of the ∼0.32 Kb Acc I- Pvu II restriction fragment are obtained and suspended in 7 µl of H₂O. About 0.25 µg (in 0.5 µl) of Bcl I linkers (5'-CTGATCAG-3', available from New England Biolabs), were kinased and prepared for ligation by the following procedure. Four µl of linkers (∼2 µg) were dissolved in 20.15 µl of H₂O and 5 µl of 10X kinase buffer (500 mM Tris-HCl, pH=7.6 and 100 mM MgCl₂), incubated at 90°C for two minutes, and then cooled to room temperature. Five µl of [γ-³²P]-ATP (∼20 µCi), 2.5 µl of 1 M DTT, and 5 µl of polynucleotide kinase (∼10 units) were added to the mixture, which was then incubated at 37°C for 30 minutes. Then, 3.35 µl of 0.01 M ATP and 5 µl of kinase were added, and the reaction was continued for another 30 minutes at 37°C. The radioactive ATP aids in determining whether the linkers have ligated to the target DNA. The kinased linkers were added to the solution of the ∼0.32 kb Acc I- Pvu II restriction fragment before 1 µl (∼1000 units) of T4 DNA ligase and 1 µl of 10X ligase buffer were added to the solution of DNA. The resulting reaction was incubated at 16°C overnight. The Bcl I linkers could only ligate to the Pvu II end of the Acc I- Pvu II restriction fragment. DNA sequencing later revealed that four Bcl I linkers attached to the Pvu II end of the Acc I- Pvu II restriction fragment. These extra Bcl I linkers can be removed by Bcl I digestion and religation; however, the extra Bcl I linkers were not removed as the linkers do not interfere with the proper functioning of the vectors. E . coli K12 HB101/pSV2cat cells are obtained in lyophilized form from the ATCC under the accession number ATCC 37155, and plasmid pSV2cat DNA was isolated from the cells. A restriction site and function map of plasmid pSV2cat is presented in Figure 5 of the accompanying drawings. About 1 mg of plasmid pSV2cat DNA is obtained and dissolved in 1 ml of TE buffer. About 3 µg (3 µl) of the plasmid pSV2cat DNA were added to 2 µl of 10X Acc I buffer and 16 µl of H₂O, and then, 3 µl (about 9 units) of restriction enzyme Acc I were added to the solution of pSV2cat DNA, and the resulting reaction was incubated at 37°C for 2 hours. The Acc I-digested plasmid pSV2cat DNA was then digested with restriction enzyme Stu I by adding 3 µl of 10X Stu I buffer (1.0 M NaCl; 100 mM Tris-HCl, pH=8.0; 100 mM MgCl₂; 60 mM DTT; and 1 mg/ml BSA), 5 µl of H₂O, and about 2 µl (about 10 units) of restriction enzyme Stu I. The resulting reaction was incubated at 37°C for 2 hours. The reaction was terminated by extracting the reaction mixture once with phenol, then twice with chloroform. About 0.5 µg of the desired fragment was obtained and dissolved in 20 µl of TE buffer. About 4 µl of the Acc I- Stu I-digested plasmid pSV2cat DNA were mixed with about 7 µl of the ∼0.32 Kb Acc I- Pvu II (with Bcl I linkers attached) restriction fragment of Ad2, and after the addition of 3 µl of 10X ligase buffer, 15 µl of H₂O, and 2 µl (about 1000 units) of T4 DNA ligase, the ligation reaction was incubated at 16°C overnight. The ligated DNA constituted the desired plasmid pLPcat, a plasmid that comprises the Ad2 late promoter positioned so as to drive transcription, and thus expression, of the chloramphenicol acetyltransferase gene. A restriction site and function map of plasmid pLPcat is presented in Figure 6 of the accompanying drawings. The ligated DNA was used to transform E . coli K12 HB101 cells and the transformed cells were plated on L agar containing 50 µg/ml ampicillin; restriction enzyme analysis of plasmid DNA was used to identify the E . coli K12 HB101/pLPcat transformants. Plasmid pLPcat DNA was then isolated from the transformants for use in subsequent vector constructions. B. Final Construction of Plasmid pBLcat About 88 µg of plasmid pBKneo1 DNA in 50 µl of TE buffer were added to 7.5 µl of 10X Acc I buffer, 30 µl of H₂O, and 15 µl (about 75 units) of restriction enzyme Acc I, and the resulting reaction was incubated at 37°C for 2 hours. The Acc I-digested BK virus DNA was loaded on an agarose gel, and the ∼1.4 Kb fragment that contains the BK enhancer was separated from the other digestion products. The ∼1.4 Kb Acc I restriction fragment was then isolated in substantial accordance with the procedure described in Example 9. About 5 µg of the fragment were resuspended in 5 µl of 10X Pvu II buffer, 45 µl of H₂O, and 5 µl (about 25 units) of restriction enzyme Pvu II, and the resulting reaction was incubated at 37°C for 2 hours. The Pvu II-digested DNA was then isolated and prepared for ligation in substantial accordance with the procedure of Example 9. About 2 µg of the desired ∼1.28 Kb Acc I- Pvu II fragment were obtained and dissolved in 5 µl of TE buffer. About 1 µg of plasmid pLPcat DNA was dissolved in 5 µl of 10X Acc I buffer and 40 µl of H₂O. About 5 µl (∼25 units) of restriction enzyme Acc I were added to the solution of plasmid pLPcat DNA, and the resulting reaction was incubated at 37°C. The Acc I-digested plasmid pLPcat DNA was precipitated with ethanol and resuspended in 5 µl of 10X Stu I buffer, 40 µl of H₂O, and 5 µl (about 25 units) of restriction enzyme Stu I, and the resulting reaction was incubated at 37°C for 2 hours. The Acc I- Stu I-digested plasmid pLPcat DNA was precipitated with ethanol several times to purify the ∼4.81 Kb Acc I- Stu I restriction fragment that comprises the E . coli origin of replication and Ad2 late promoter away from the other digestion product, a restriction fragment about 16 bp in size. About 1 µg of the desired ∼4.81 Kb restriction fragment was obtained and dissolved in 20 µl of TE buffer. The 5 µl of ∼4.81 Kb Acc I- Stu I restriction fragment of plasmid pLPcat were added to 5 µl of ∼1.28 Kb Acc I- Pvu II restriction fragment of BK virus. After the addition of 3 µl of 10X ligase buffer, 15 µl of H₂O, and 2 µl (about 1000 units) of T4 DNA ligase to the mixture of DNA, the resulting ligation reaction was incubated at 16°C overnight. The ligated DNA constituted the desired plasmid pBLcat. A restriction site and function map of plasmid pBLcat is presented in Figure 7 of the accompanying drawings. The ligated DNA was used to transform E . coli K12 HB101 cells and E . coli K12 HB101/pBLcat transformants were identified by restriction enzyme analysis of their plasmid DNA. Next, plasmid pBLcat DNA was prepared for use in subsequent vector constructions. Example 12 Construction of Plasmid pL133 A. Construction of Intermediate Plasmid pSV2-HPC8 Plasmid pHC7 comprises a DNA sequence that encodes human protein C. One liter of L-broth containing 15 µg/ml tetracycline was inoculated with a culture of E . coli K12 RR1/pHC7 (NRRL B-15926), and plasmid pHC7 DNA was isolated and purified in substantial accordance with the procedure of Example 10. About 1 mg of plasmid pHC7 DNA was obtained by this procedure, suspended in 1 ml of TE buffer, and stored at -20°C. A restriction site and function map of plasmid pHC7 is presented in Figure 8 of the accompanying drawings. Fifty µl of the plasmid pHC7 DNA were mixed with 5 µl (∼50 units) of restriction enzyme Ban I, 10 µl of 10X Ban I reaction buffer (1.5 M NaCl; 60 mM Tris-HCl, pH=7.9; 60 mM MgCl₂; and 1 mg/ml BSA), and 35 µl of H₂O and incubated until the digestion was complete. The Ban I-digested plasmid pHC7 DNA was then electrophoresed on a 3.5% polyacrylamide gel, until the ∼1.25 Kb Ban I restriction fragment was separated from the other digestion products. The region of the gel containing the ∼1.25 Kb Ban I restriction fragment was isolated according to the teaching of Example 3. Approximately 8 µg of the ∼1.25 Kb Ban I restriction fragment were obtained by this procedure. The purified fragment was suspended in 10 µl of TE buffer and stored at -20°C. The Ban I restriction fragment had to be modified by the addition of a linker to construct plasmid pSV2-HPC8. The DNA fragments used in the construction of the linker were synthesized either by using a Systec 1450A DNA Synthesizer or an ABS 380A DNA Synthesizer. Five hundred picomoles of each single strand of the linker were kinased in 20 µl of reaction buffer, which contained 15 units (∼0.5 µl) T4 polynucleotide kinase, 2 µl 10X ligase buffer, 10 µl of 500 µM ATP, and 7.5 µl of H₂O. The kinase reaction was incubated at 37°C for 30 minutes, and the reaction was terminated by incubation at 100°C for 10 minutes. In order to ensure complete kination, the reaction was chilled on ice, 2 µl of 0.2 M dithiothreitol, 2.5 µl of 5 mM ATP, and 15 units of T4 polynucleotide kinase were added to the reaction mixture and mixed, and the reaction mixture was incubated another 30 minutes at 37°C. The reaction was stopped by another 10 minute incubation at 100°C and then chilled on ice. Although kinased separately, the two single strands of the DNA linker were mixed together after the kinase reaction. To anneal the strands, the kinase reaction mixture was incubated at 100°C for 10 minutes in a water bath containing ∼150 ml of water. After this incubation, the water bath was shut off and allowed to cool to room temperature, a process taking about 3 hours. The water bath, still containing the tube of kinased DNA, was then incubated at 4°C overnight. This process annealed the single strands. The linker constructed had the following structure: The linker was stored at -20°C until use. The ∼8 µg of ∼1.25 Kb Ban I fragment were added to and mixed with the ∼50 µl of linker (∼500 picomoles), 1 µl of T4 DNA ligase (∼500 units), 10 µl of 10X ligase buffer, and 29 µl of H₂O, and the resulting ligation reaction was incubated at 4°C overnight. The ligation reaction was stopped by a 10 minute incubation at 65°C. The DNA was pelleted by adding NaOAc to a final concentration of 0.3 M, adding 2 volumes of ethanol, chilling in a dry ice-ethanol bath, and then centrifuging the solution. The DNA pellet was dissolved in 10 µl of 10X Apa I reaction buffer (60 mM NaCl; 60 mM Tris-HCl, pH=7.4; 60 mM MgCl₂; and 60 mM 2-mercaptoethanol), 5 µl (∼50 units) of restriction enzyme Apa I, and 85 µl of H₂O, and the reaction was placed at 37°C for two hours. The reaction was then stopped and the DNA pelleted as above. The DNA pellet was dissolved in 10 µl of 10X Hin dIII reaction buffer, 5 µl (∼50 units) of restriction enzyme Hin dIII, and 85 µl of H₂O, and the reaction was placed at 37°C for two hours. After the Hin dIII digestion, the reaction mixture was loaded onto a 3.5% polyacrylamide gel, and the desired ∼1.23 Kb Hin dIII- Apa I restriction fragment was isolated. Approximately 5 µg of the desired fragment were obtained, suspended in 10 µl of TE buffer, and stored at -20°C. Fifty µl of plasmid pHC7 DNA were mixed with 5 µl (∼50 units) of restriction enzyme Pst I, 10 µl of 10X Pst I reaction buffer (1.0 M NaCl; 100 mM Tris-HCl, pH=7.5; 100 mM MgCl₂; and 1 mg/ml BSA), and 35 µl of H₂O and incubated at 37°C for two hours. The Pst I-digested plasmid pHC7 DNA was then electrophoresed on a 3.5% polyacrylamide gel, and the desired ∼0.88 Kb fragment was purified in substantial accordance with the procedure described above. Approximately 5 µg of the desired fragment were obtained, suspended in 10 µl of TE buffer, and stored at -20°C. The ∼5 µg of ∼0.88 Kb Pst I fragment were added to and mixed with ∼50 µl of the following linker, which was constructed on an automated DNA synthesizer: About 1 µl of T4 DNA ligase (∼10 units), 10 µl 10X ligase buffer, and 29 µl H₂O were added to the mixture of DNA, and the resulting ligation reaction was incubated at 4°C overnight. The ligation reaction was stopped by a 10 minute incubation at 65°C. After precipitation of the ligated DNA, the DNA pellet was dissolved in 10 µl of 10X Apa I reaction buffer, 5 µl (∼50 units) of restriction enzyme Apa I, and 85 µl of H₂O, and the reaction was placed at 37° for two hours. The reaction was then stopped and the DNA pelleted once again. The DNA pellet was dissolved in 10 µl 10X Bgl II reaction buffer (1 M NaCl; 100 mM Tris-HCl, pH=7.4; 100 mM MgCl₂; 100 mM 2-mercaptoethanol; and 1 mg/ml BSA), 5 µl (∼50 units) of restriction enzyme Bgl II, and 85 µl H₂O, and the reaction was placed at 37°C for two hours. After the Bgl II digestion, the reaction mixture was loaded onto a 3.5% polyacrylamide gel to isolate the desired ∼0.19 Kb Apa I- Bgl II restriction fragment. Approximately 1 µg of the desired fragment was obtained, suspended in 10 µl of TE buffer, and stored at -20°C. Approximately 10 µg of plasmid pSV2gpt DNA (ATCC 37145) were dissolved in 10 µl of 10X Hin dIII reaction buffer, 5 µl (∼50 units) of restriction enzyme Hin dIII, and 85 µl of H₂O, and the reaction was placed at 37°C for 2 hours. The reaction mixture was then made 0.25 M in NaOAc, and after the addition of two volumes of ethanol and incubation in a dry ice-ethanol bath, the DNA was pelleted by centrifugation. The DNA pellet was dissolved in 10 µl of 10X Bgl II buffer, 5 µl (∼50 units) of restriction enzyme Bgl II, and 85 µl of H₂O, and the reaction was placed at 37°C for two hours. After the Bgl II digestion, the reaction mixture was loaded onto a 1% agarose gel, and the fragments were separated by electrophoresis. The gel was stained with ethidium bromide and viewed under ultraviolet light, and the band containing the desired ∼5.1 Kb Hin dIII- Bgl II fragment was cut from the gel and placed in dialysis tubing, and electrophoresis was continued until the DNA was out of the agarose. The buffer containing the DNA from the dialysis tubing was extracted with phenol and CHCl₃, and then, the DNA was precipitated. The pellet was resuspended in 10 µl of TE buffer and constituted ∼5 µg of the desired ∼5.1 Kb Hin dIII- Bgl II restriction fragment of plasmid pSV2gpt. Two µl of the ∼1.23 Kb Hin dIII- Apa I restriction fragment, 3 µl of the ∼0.19 Kb Apa I- Bgl II fragment, and 2 µl of the ∼5.1 Kb Hin dIII- Bgl II fragment were mixed together and then incubated with 10 µl of 10X ligase buffer, 1 µl of T4 DNA ligase (∼500 units), and 82 µl of H₂O at 16°C overnight. The ligated DNA constituted the desired plasmid pSV2-HPC8; a restriction site and function map of the plasmid is presented in Figure 8 of the accompanying drawings. E . coli K12 RR1 (NRRL B-15210) cells were made competent for transformation and the ligated DNA prepared above was used to transform the cells. Aliquots of the transformation mix were plated on L-agar plates containing 100 µg/ml ampicillin. The plates were then incubated at 37°C. E . coli K12 RR1/pSV2-HPC8 transformants were verified by restriction enzyme analysis of their plasmid DNA. B. Final Construction of Plasmid pL133 Fifty µg of plasmid pSV2-HPC8 were dissolved in 10 µl of 10X Hin dIII reaction buffer, 5 µl (∼50 units) of restriction enzyme Hin dIII, and 85 µl of H₂O, and the reaction was incubated at 37°C for two hours. After the Hin dIII digestion, the DNA was precipitated, and the DNA pellet was dissolved in 10 µl 10X Sal I reaction buffer (1.5 M NaCl; 60 mM Tris-HCl, pH=7.9; 60 mM MgCl₂; 60 mM 2-mercaptoethanol; and 1 mg/ml BSA), 5 µl (∼50 units) of restriction enzyme Sal I, and 85 µl of H₂O. The resulting Sal I reaction mixture was incubated for 2 hours at 37°C. The Hin dIII- Sal I-digested plasmid pSV2-HPC8 was loaded onto a 3.5% polyacrylamide gel and electrophoresed until the desired ∼0.29 Kb Hin dIII- Sal I restriction fragment was separated from the other reaction products. The desired fragment was isolated from the gel; about 2 µg of the fragment were obtained and suspended in 10 µl of TE buffer. Fifty µg of plasmid pSV2-HPC8 were dissolved in 10 µl of 10X Bgl II reaction buffer, 5 µl (50 units) of restriction enzyme Bgl II, and 85 µl of H₂O, and the reaction was incubated at 37°C for two hours. After the Bgl II digestion, the DNA was precipitated, and the DNA pellet was dissolved in 10 µl of 10X Sal I reaction buffer, 5 µl (∼50 units) of restriction enzyme Sal I, and 85 µl of H₂O. The resulting Sal I reaction mixture was incubated for 2 hours at 37°C. The Sal I- Bgl II-digested plasmid pSV2-HPC8 was loaded onto a 3.5% polyacrylamide gel and electrophoresed until the desired ∼1.15 Kb Sal I- Bgl II restriction fragment was separated from the other reaction products. The ∼1.15 Kb Sal I- Bgl II restriction fragment was isolated from the gel; about 8 µg of fragment were obtained and suspended in 10 µl of TE buffer. Approximately 10 µg of plasmid pSV2-β-globin DNA (NRRL B-15928) were dissolved in 10 µl of 10X Hin dIII reaction buffer, 5 µl (∼50 units) of restriction enzyme Hin dIII, and 85 µl of H₂O, and the reaction was placed at 37°C for 2 hours. The reaction mixture was then made 0.25 M in NaOAc, and after the addition of two volumes of ethanol and incubation in a dry ice-ethanol bath, the DNA was pelleted by centrifugation. The Hin dIII-digested plasmid pSV2-β-globin was dissolved in 10 µl of 10X Bgl II buffer, 5 µl (∼50 units) of restriction enzyme Bgl II, and 85 µl of H₂O, and the reaction was placed at 37°C for two hours. After the Bgl II digestion, the reaction mixture was loaded onto a 1% agarose gel, and the fragments were separated by electrophoresis. The desired ∼4.2 Kb Hin dIII- Bgl II restriction fragment was isolated from the gel; about 5 µg of the desired fragment were obtained and suspended in 10 µg of TE buffer. Two µg of the ∼0.29 Kb Hin dIII- Sal I fragment of plasmid pSV2-HPC8, 2 µl of the ∼1.15 Kb Sal I- Bgl II fragment of plasmid pSV2-HPC8, and 2 µl of the ∼4.2 Kb Hin dIII- Bgl II fragment of plasmid pSV2-β-globin were mixed together and ligated in substantial accordance with the procedure of Example 12A. The ligated DNA constituted the desired plasmid pL133; Figure 8 illustrates by flow chart the construction of plasmid pL133 from the various starting materials described throughout this example. The desired E . coli K12 RR1/pL133 transformants were constructed and plasmid DNA was isolated for use in the construction of plasmid pLPC. Example 13 Construction of Plasmid pLPC About 20 µg of plasmid pBLcat DNA were dissolved in 10 µl of 10X Hin dIII buffer and 80 µl of H₂O. About 10 µl (∼100 units) of restriction enzyme Hin dIII were added to the solution of plasmid pBLcat DNA, and the resulting reaction was incubated at 37°C for 2 hours. The Hin dIII-digested plasmid pBLcat DNA was loaded onto an agarose gel and electrophoresed until the ∼0.87 Kb Hin dIII restriction fragment that comprises the BK enhancer and Ad2 late promoter was separated from the other digestion products; then, the ∼0.87 Kb fragment was isolated and prepared for ligation in substantial accordance with the procedure of Example 9. About 2 µg of the desired fragment were obtained and dissolved in 5 µl of TE buffer. About 1.5 µg of plasmid pL133 DNA was dissolved in 2 µl of 10X Hin dIII buffer and 16 µl of H₂O. About 1 µl (∼10 units) of restriction enzyme Hin dIII was added to the solution of DNA, and the resulting reaction was incubated at 37°C for 2 hours. The DNA was then diluted to 100 µl with TE buffer and treated with calf-intestinal alkaline phosphatase in substantial accordance with the procedure in Example 9. The Hin dIII-digested plasmid pL133 DNA was extracted twice with phenol and once with chloroform, precipitated with ethanol, and resuspended in 10 µl of TE buffer. About 5 µl of the ∼0.87 Kb Hin dIII restriction fragment of plasmid pBLcat were added to the 1.5 µl of Hin dIII-digested plasmid pL133, and then, 1 µl of 10X ligase buffer, 1 µl (∼1000 units) of T4 DNA ligase, and 1.5 µl of H₂O were added to the solution of DNA, and the resulting reaction was incubated at 16°C overnight. The ligated DNA constituted the desired plasmid pLPC. The ligated DNA was used to transform E . coli K12 HB101. The transformed cells were plated on L agar containing ampicillin, and the plasmid DNA of the ampicillin-resistant transformants was examined by restriction enzyme analysis to identify the E . coli K12 HB101/pLPC transformants. The ∼0.87 Kb Hin dIII restriction fragment that encodes the BK enhancer and Ad2 late promoter could insert into Hin dIII-digested plasmid pSBLcat in one of two orientations, only one of which yields plasmid pLPC. A restriction site and function map of plasmid pLPC is presented in Figure 9 of the accompanying drawings. Example 14 Construction of Plasmids pLPC4 and pLPC5 About 1 µg (1 µl) of the BK virus DNA prepared in Example 8 and 1 µg of plasmid pLPC (1 µl) were dissolved in 2 µl of 10X Eco RI buffer and 14 µl of H₂O. About 2 µl (∼10 units) of restriction enzyme Eco RI were added to the solution of DNA, and the resulting reaction was incubated at 37°C for 2 hours. The Eco RI-digested mixture of BK virus and plasmid pLPC DNA was extracted once with buffered phenol and once with chloroform. Then, the DNA was collected by adjusting the NaCl concentration to 0.25 M, adding two volumes of ethanol, incubating the solution in a dry ice-ethanol bath for 2 minutes, and centrifuging the solution to pellet the DNA. The supernatant was discarded, and the DNA pellet was rinsed with 70% ethanol, dried, and resuspended in 12 µl of TE buffer. About 13 µl of H₂O and 3 µl of 10X ligase buffer were added to the Eco RI-digested mixture of BK virus and plasmid pLPC DNA. Two µl (∼1000 units) of T4 DNA ligase were added to the solution of DNA, and the resulting reaction was incubated at 16°C for 2 hours. The ligated DNA, constituting the desired plasmids pLPC4 and pLPC5, which differ only with respect to the orientation of the inserted BK virus DNA, was used to transform E . coli K12 HB101 competent cells. The transformed cells were plated on L agar containing 100 µg/ml ampicillin. The E . coli K12 HB101/pLPC4 and E . coli K12 HB101/pLPC5 transformants were identified by their ampicillin-resistant phenotype and by restriction enzyme analysis of their plasmid DNA. A restriction site and function map of plasmid pLPC4 is presented in Figure 10 of the accompanying drawings. Example 15 Construction of Plasmids pLPChyg1 and pLPChyg2 E . coli K12 RR1/pSV2hyg cells are obtained from the NRRL under the accession number NRRL B-18039. Plasmid pSV2hyg DNA is obtained from the cells in substantial accordance with the procedure of Example 10. A restriction site and function map of plasmid pSV2hyg is presented in Figure 11 of the accompanying drawings. About 10 µg (in 10 µl of TE buffer) of plasmid pSV2hyg were added to 2 µl of 10X Bam HI buffer and 6 µl of H₂O. About 2 µl (about 20 units) of restriction enzyme Bam HI were added to the solution of DNA, and the resulting reaction was incubated at 37°C for 2 hours. The reaction was extracted first with phenol and then was extracted twice with chloroform. The Bam HI-digested plasmid pSV2hyg DNA was loaded onto an agarose gel to isolate the ∼2.5 Kb restriction fragment containing the hygromycin resistance gene. About 5 µl of 10X Klenow buffer (0.2 mM in each of the four dNTPs; 0.5 M Tris-HCl, pH=7.8; 50 mM MgCl₂; 0.1 M 2-mercaptoethanol; and 100 µg/ml BSA) and 35 µl of H₂O were added to the solution of Bam HI-digested plasmid pSV2hyg DNA, and then, about 25 units of Klenow enzyme (about 5 µl, as marketed by BRL) were added to the mixture of DNA, and the resulting reaction was incubated at 16°C for 30 minutes. The Klenow-treated, Bam HI-digested plasmid pSV2hyg DNA was extracted once with phenol and once with chloroform and then precipitated with ethanol. About 2 µg of the desired fragment were obtained and suspended in 5 µl of TE buffer. About 10 µg (10 µl) of plasmid pLPC DNA were added to 2 µl of 10X Stu I buffer and 6 µl of H₂O. About 2 µl (∼10 units) of restriction enzyme Stu I were added to the solution of DNA, and the resulting reaction was incubated at 37°C for 2 hours. The Stu I-digested plasmid pLPC DNA was precipitated with ethanol, collected by centrifugation, and resuspended in 2 µl of 10X Nde I buffer (1.5 M NaCl; 0.1 M Tris-HCl, pH=7.8; 70 mM MgCl₂; 60 mM 2-mercaptoethanol; and 1 mg/ml BSA) and 16 µl of H₂O. About 2 µl (∼10 units) of restriction enzyme Nde I were added to the solution of Stu I-digested DNA, and the resulting reaction was incubated at 37°C for 2 hours. The Nde I- Stu I-digested plasmid pLPC DNA was precipitated with ethanol, collected by centrifugation, and resuspended in 5 µl of 10X Klenow buffer and 40 µl of H₂O. About 5 µl (∼25 units) of Klenow enzyme were added to the solution of DNA, and the resulting reaction was incubated at 16°C for 30 minutes. After the Klenow reaction, the reaction mixture was loaded onto an agarose gel, and the ∼5.82 Kb Nde I- Stu I restriction fragment was isolated from the gel. About 5 µg of the desired fragment were obtained and suspended in 5 µl of TE buffer. About 2 µl of the ∼2.5 Kb Klenow-treated Bam HI restriction fragment of plasmid pSV2hyg were mixed with about 1 µl of the ∼5.82 Kb Klenow-treated Nde I- Stu I restriction fragment of plasmid pLPC, and about 3 µl of 10X ligase buffer, 2 µl of T4 DNA ligase (∼1000 units), 1 µl of T4 RNA ligase (∼1 unit), and 14 µl of H₂O were added to the solution of DNA. The resulting reaction was incubated at 16°C overnight. The ligated DNA constituted the desired plasmids pLPChyg1 and pLPChyg2, which differ only with respect to the orientation of the ∼2.5 Kb Klenow-treated, Bam HI restriction fragment of plasmid pSV2hyg. A restriction site and function map of plasmid pLPChyg1 is presented in Figure 12 of the accompanying drawings. The ligated DNA was used to transform E . coli K12 HB101 and the desired E . coli K12 HB101/pLPChyg1 and E . coli K12 HB101/pLPChyg2 transformants were plated on L agar containing ampicillin and identified by restriction enzyme analysis of their plasmid DNA. Example 16 Construction of Plasmids pLPChd1 and pLPChd2 About 20 µg of plasmid pSV2-dhfr (ATCC 37146) in 20 µl of TE buffer is added to 10 µl of 10X Bam HI buffer and 60 µl of H₂O. About 10 µl (∼50 units) of restriction enzyme Bam HI are added and the resulting reaction is incubated at 37°C for two hours. The Bam HI-digested plasmid DNA is then precipitated with ethanol, collected by centrifugation, and resuspended in 5 µl of 10X Klenow buffer, 45 µl of H₂O, and 2 µl (∼100 units) of Klenow enzyme. The reaction is incubated at 16°C for 30 minutes and then the reaction mixture is loaded onto an agarose gel and electrophoresed until the digestion products are clearly separated. The ∼1.9 Kb Klenow-treated, Bam HI restriction fragment that comprises the dhfr gene is isolated from the gel and prepared for ligation in substantial accordance with the procedure of Example 9. About 4 µg of the desired fragment are obtained and suspended in 5 µl of TE buffer. About 200 µg of plasmid pLPChyg1 in 100 µl of TE buffer were added to 15 µl of 10X Eco RI buffer and 30 µl of H₂O. About 5 µl (∼50 units) of restriction enzyme Eco RI were added to the solution of plasmid pLPChyg1 DNA, and the resulting reaction was incubated at 37°C for about 10 minutes. The short reaction time was calculated to produce a partial Eco RI digestion. Plasmid pLPChyg1 has two Eco RI restriction sites, one of which is within the coding sequence of the hygromycin resistance-conferring (HmR) gene, and it was desired to insert the dhfr-gene-containing restriction fragment into the Eco RI site of plasmid pLPChyg1 that is not in the HmR gene. The partially- Eco RI-digested plasmid pLPChyg1 DNA was loaded onto an agarose gel and electrophoresed until the singly-cut plasmid pLPChyg1 DNA was separated from uncut plasmid DNA and the other digestion products. The singly-cut DNA was isolated from the gel and prepared for ligation in substantial accordance with the procedure of Example 9. About 2 µg of the singly- Eco RI-cut plasmid pLPChyg1 were obtained and suspended in 25 µl of TE buffer. To this sample, about 5 µl (∼25 units) of Klenow enzyme, 5 µl of 10X Klenow buffer, and 40 µl of H₂O were added, and the resulting reaction was incubated at 16°C for 60 minutes. The Klenow-treated, partially- Eco RI-digested DNA was then extracted twice with phenol and then once with chloroform, precipitated with ethanol, and resuspended in 25 µl of TE buffer. About 5 µl of the ∼1.9 Kb Klenow-treated Bam HI restriction fragment containing the dhfr gene and about 5 µl of the singly- Eco RI-cut plasmid pLPChyg1 DNA were mixed together, and 1 µl of 10X ligase buffer, 5 µl of H₂O, 1 µl (∼500 units) of T4 DNA ligase, and 1 µl (∼2 units) of T4 RNA ligase were added to the mixture of DNA, and the resulting reaction was incubated at 16°C overnight. The ligated DNA constituted the desired plasmids pLPChd1 and pLPChd2, which differ only with respect to the orientation of the ∼1.9 Kb fragment that comprises the dhfr gene. The ligated DNA was used to transform competent E . coli K12 HB101 cells. The transformed cells were plated onto L agar containing 100 µg/ml ampicillin, and the ampicillin-resistant transformants were analyzed by restriction enzyme analysis of their plasmid DNA to identify the E . coli K12 HB101/pLPChd1 and E . coli K12 HB101/pLPChd2 transformants. A restriction site and function map of plasmid pLPChd1 is presented in Figure 13 of the accompanying drawings. Plasmid pLPChd1 and plasmid pLPChd2 DNA were subsequently isolated from the appropriate transformants. Example 17 Construction of Plasmid phd To construct plasmid phd, it was necessary to prepare the plasmid pLPChd1 DNA, used as starting material in the construction of plasmid phd, from E . coli host cells that lack an adenine methylase, such as that encoded by the dam gene, the product of which methylates the adenine residue in the sequence 5'-GATC-3'. E . coli K12 GM48 (NRRL B-15725) lacks a functional dam methylase and so is a suitable host to use for the purpose of preparing plasmid pLPChd1 DNA for use as starting material in the construction of plasmid phd. E . coli K12 GM48 cells were cultured and made competent for transformation, and plasmid pLPChyg1 was used to transform the E . coli K12 GM48 cells. The transformed cells were plated on L agar containing ampicillin, and once the ampicillin-resistant, E . coli K12 GM48/pLPChd1 transformants had formed colonies, one such colony was used to prepare plasmid pLPChd1 DNA. About 1 mg of plasmid pLPChd1 DNA was obtained and suspended in about 1 ml of TE buffer. About 2 µg of plasmid pLPChd1 DNA in 2 µl of TE buffer were added to 2 µl of 10X Bcl I buffer (750 mM KCl; 60 mM Tris-HCl, pH=7.4; 100 mM MgCl₂; 10 mM DTT and 1 mg/ml BSA) and 14 µl of H₂O. About 2 µl (∼10 units) of restriction enzyme Bcl I were added to the solution of plasmid pLPChd1 DNA, and the resulting reaction was incubated at 50°C for two hours. The reaction was stopped by extracting the mixture once with phenol and twice with chloroform. About 1 µl of the Bcl I-digested plasmid pLPChd1 DNA was added to 1 µl of 10X ligase buffer, 8 µl of H₂O and 1 µl (∼500 units) of T4 DNA ligase. The ligation reaction was incubated at 16°C overnight, and the ligated DNA constituted the desired plasmid phd. Plasmid phd results from the deletion of the extra Bcl I linkers that attached during the construction of plasmid pLPcat and the two adjacent Bcl I restriction fragments of a total size of about 1.45 Kb from plasmid pLPChd1. A restriction site and function map of plasmid phd is presented in Figure 14 of the accompanying drawings. Plasmid phd facilitates the expression of any DNA sequence from the BK virus enhancer-adenovirus late promoter of the present invention, because the DNA to be expressed, such as human protein S, can be readily inserted in the correct position for expression at the single Bcl I site on plasmid phd. The ligated DNA was used to transform E . coli K12 GM48 and the transformed cells were plated on L-agar containing ampicillin. The ampicillin-resistant E . coli K12 GM48/phd transformants were identified by restriction enzyme analysis of their plasmid DNA. Example 18 Construction of Human Protein S Expression Vectors A. Construction of Plasmid pShd About 2 µg of plasmid phd DNA in 2 µl of TE buffer were digested with Bcl I restriction enzyme in substantial accordance with the teaching of Example 17. The Bcl I-digested plasmid DNA was precipitated with ethanol, collected by centrifugation, and resuspended in 5 µl of 10X Klenow buffer and 40 µl of H₂O. About 5 µl (∼25 units) of Klenow enzyme were added to the solution of DNA and the resulting reaction was incubated at 16°C for 30 minutes. After the Klenow reaction, the reaction mixture was loaded onto an agarose gel and the vector fragment was isolated from the gel. About 0.5 µg of the desired fragment were obtained and suspended in 10 µl of TE buffer. Approximately 20 µg of plasmid pHHS-IIa DNA were dissolved in 10 µl of 10X Fnu DII reaction buffer, 10 µl (∼20 units) of restriction enzyme Fnu DII, and 80 µl of H₂O, and the reaction mixture was placed at 37°C for two hours. The reaction was adjusted by adding NaCl to 50 mM and 5 µl (∼50 units) of restriction enzyme Eco RV. The resulting reaction was incubated at 37°C for two hours. After the Eco RV digestion, the reaction mixture was loaded onto a 1.0% agarose gel to isolate the desired ∼2.7 Kb Fnu DII- Eco RV restriction fragment. Approximately 10 µg of the fragment were obtained and suspended in 50 µl of TE buffer. About 5 µl of the Bcl I-digested plasmid phd were ligated to about 2 µl of the ∼2.7 Kb Fnu DII- Eco RV restriction fragment in substantial accordance with the teaching of preceding examples except that ∼0.4 units of RNA ligase (BRL) was added to the ligation reaction. The ligated DNA constituted the desired plasmid pShd; a restriction site and function map of the plasmid is presented in Figure 1 of the accompanying drawings. E . coli K12 HB101 cells were made competent for transformation and the ligated DNA prepared above was used to transform the cells. Aliquots of the transformation mix were plated on L-agar containing ampicillin. The ampicillin-resistant E . coli K12 HB101/pShd transformants were identified by restriction enzyme analysis. Alternatively, should one wish to isolate a fragment that contains only the protein S coding sequence, the additional base pairs can be removed from the 5' end of the molecule to produce a molecule that begins with the ATG start codon. Thus, linear DNA can be digested with an exonuclease called BAL 31 nuclease that attacks both ends of the molecule and progressively shortens the molecule at a predictable rate. Accordingly, five µg of pHHS-IIa are digested with 5 units of Fnu DII in 100 µl of 6 mM NaCl, 6 mM Tris-HCl (pH=7.4), 6 µM MgCl₂, and 6 µM 2-mercaptoethanol. Following an ethanol precipitation, the DNA fragments are separated by electrophoresis on a 3.5% polyacrylamide gel and the 2.7 Kb fragment is isolated as described in Example 3. The fragment is now prepared for digestion with BAL 31. The reaction conditions are as follows: 5 µg of DNA is dissolved in 50 µl of 0.5 M NaCl, 12.5 mM CaCl₂, 12.5 mM MgCl₂, 20 mM Tris-HCl, pH=8.0, and 1 mM EDTA, pH=8.0. One unit of BAL 31 is added and the reaction is allowed to continue at 30°C for 30 seconds. Following an ethanol precipitation, the DNA is now treated with T4 DNA polymerase to fill in any staggered ends that may have been left by the action of the BAL 31. The DNA is resuspended in 19 µl of reaction buffer (16.6 mM (NH₄)₂SO₄, 0.67 M Tris-HCl, pH=8.8, 0.67 mM MgCl₂, 1 M 2-mercaptoethanol, and 6.7 µM EDTA). To this is added 1 µl of T4 DNA polymerase (0.5 units) diluted 1 to 10 in 50 mM Tris-HCl, pH=7.5, 100 mM (NH₄)₂SO₄, 1 mg/ml BSA and 10 mM 2-mercaptoethanol. The reaction is incubated for 10 minutes at 37°C before the addition of 1 µl of a dNTP mix containing 2 mM of each dNTP. The reaction continues at 37°C for an additional 10 minutes followed by an ethanol precipitation. This fragment is now ready to ligate to any blunt-end vector. Under these conditions BAL 31 removes about 25 base pairs/minute/end. After ligation, transformation into an E . coli host and subsequent isolation of DNA from independent clones, one can use DNA sequencing to determine which clone contains the exact sequence desired. The plasmid pHHS-IIa also contains additional non-coding DNA sequences at the 3' end, including the natural stop codon TAA which immediately follows the last nucleotide triplet of the coding sequence. These sequences can be removed as follows: 5 µg of the intact plasmid are digested to completion in 100 µl of 1X Fnu DII reaction buffer containing 5 units of Fnu dII. The DNA is precipitated in ethanol and recovered by centrifugation. The pellet is dried and resuspended in 100 µl of 1X Eco RI reaction buffer containing 5 units of Eco RI. After 90 minutes at 37°C, the DNA is again precipitated in ethanol and is applied to a 3.5% polyacrylamide gel. The products are separated by electrophoresis and the ∼2030 base pair band is extracted as described in Example 3. Since the Eco RI site is located only one base away from the natural stop codon, and digestion with Eco RI leaves only the initial G residue, it is necessary to replace the remaining bases of the Eco RI site, the T residue and the stop codon. Thus, a linker has been designed for this purpose and can be synthesized by any of the standard techniques: This linker includes the natural sequence and incorporates an additional stop codon in frame to insure termination at that point. In addition, this linker contains a CTAG overhang that is compatable with Bam HI, Bgl II or Bcl I ends. In a three-piece ligation reaction these fragments can be ligated to any vector that contains one blunt end along with a Bam HI, Bgl II or Bcl I end. B Transformation The transformation procedure described below refers to 293 cells as the host cell line; however, the procedure is generally applicable to most eukaryotic cell lines. 293 cells were obtained from the ATCC under the accession number CRL 1573 in a 25 mm² flask containing a confluent monolayer of about 5.5 x 10⁶ cells in Eagle's Minimum Essential Medium with 10% heat-inactivated horse serum. The flask was incubated at 37°C; medium was changed twice weekly. The cells were sub-cultured by removing the medium, rinsing with Hank's Balanced Salts solution (Gibco), adding 0.25% trypsin for 1-2 minutes, rinsing with fresh medium, aspirating, and dispensing into new flasks at a subcultivation ratio of 1:5 or 1:10. One day prior to transformation, cells were seeded at 0.7 x 10⁶ cells per dish. The medium was changed 4 hours prior to transformation. Sterile, ethanol-precipitated plasmid DNA dissolved in TE buffer was used to prepare a 2X DNA-CaCl₂ solution containing 40 µg/ml DNA and 250 mM CaCl₂. 2X HBS was prepared containing 280 mM NaCl, 50 mM Hepes, and 1.5 mM sodium phosphate, with the pH adjusted to 7.05-7.15. The 2X DNA-CaCl₂ solution was added dropwise to an equal volume of sterile 2X HBS. A one ml sterile plastic pipette with a cotton plug was inserted into the mixing tube that contains the 2X HBS, and bubbles were introduced by blowing while the DNA was being added. The calcium-phosphate-DNA precipitate was allowed to form without agitation for 30-45 minutes at room temperature. The precipitate was then mixed by gentle pipetting with a plastic pipette, and one ml (per plate) of precipitate was added directly to the 10 ml of growth medium that covers the recipient cells. After 4 hours of incubation at 37°C, the medium was replaced with DMEM with 10% fetal bovine serum and the cells allowed to incubate for an additional 72 hours before providing selective pressure. For transformants expressing recombinant human protein S, the growth medium contains 1 to 10 µg/ml vitamin K, a cofactor required for γ-carboxylation of the protein. Hygromycin is added to the growth medium to a final concentration of about 200 µg/ml. The cells are then incubated at 37°C for 2-4 weeks with medium changes at 3 to 4 day intervals. The resulting hygromycin-resistant colonies are transferred to individual culture flasks for characterization. 293 cells are dhfr positive, so 293 transformants that contain plasmids comprising the dhfr gene are not selected solely on the basis of the dhfr-positive phenotype, which is the ability to grow in media that lacks hypoxanthine and thymine. Cell lines that do lack a functional dhfr gene and are transformed with dhfr-containing plasmids can be selected for on the basis of the dhfr+ phenotype. The use of the dihydrofolate reductase gene as a selectable marker for introducing a gene or plasmid into a dhfr-deficient cell line and the subsequent use of methotrexate to amplify the copy number of the plasmid has been well established in the literature. Although the use of dhfr as a selectable and amplifiable marker in dhfr-producing cells has not been well studied, evidence in the literature would suggest that dhfr can be used as a selectable marker in dhfr-producing cells and for gene amplification. The use of the present invention is not limited by the selectable marker used. Moreover, amplifiable markers such as metallothionein genes, adenosine deaminase genes, or members of the multigene resistance family, exemplified by P-glycoprotein, can be utilized. Although the foregoing invention has been described in some detail by way of illustration and examples for purposes of clarity and understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims.

Claims: A double-stranded deoxyribonucleic acid that encodes human protein, wherein the coding strand is: wherein R' is A is deoxyadenyl, G is deoxyguanyl, C is deoxycytidyl, and T is thymidyl. A double-stranded deoxyribonucleic acid that encodes a polypeptide with human protein S activity, wherein the coding strand is: wherein A is deoxyadenyl, G is deoxyguanyl, C is deoxycytidyl, and T is thymidyl. A recombinant DNA vector which comprises the double-stranded deoxyribonucleic acid of Claim 1 or 2. The vector of Claim 3 which is plasmid pShd produced by ligating the ∼2.7 kb protein S-containing Fnu DII- Eco RV restriction fragment from plasmid pHHS-IIa (NRRL B-18071) to Bcl I-digested Klenow-treated plasmid phd (as shown in Figure 14). The vector of Claim 3 which is plasmid pHHS-IIa (NRRL B-18071). Escherichia coli cells transformed with the vector of Claim 3, 4 or 5. A culture of cells transformed with the vector of Claim 3 or 4. The culture of Claim 7 wherein the cells are human kidney 293 cells. A process for producing human protein S which comprises culturing the culture of Claim 7 or 8 under conditions permitting expression of human protein S and recovering the expressed protein. Human protein S when produced by the process of Claim 9. A pharmaceutical composition comprising human protein S produced by the process of Claim 9 in admixture with a pharmaceutically acceptable carrier. The composition of Claim 11 which is suitable for parenteral administration.

Inventors: HOSKINS, JO ANN, LONG, GEORGE LOUIS
Applicants: ELI LILLY AND COMPANY
Application year: 1987
Main classification: C07K13
IPC codes: A61P7, C12R1, C12N15, C12N1, A61K38, C12N5, C12P21, C07K14