HCV NS3 PROTEIN FRAGMENTS HAVING HELICASE ACTIVITY AND IMPROVED SOLUBILITY

Abstract: The Hepatitis C Virus (HCV) NS3 protein contains amino acid motifs of a serine proteinase, a nucleotide triphosphatase (NTPase), and an RNA helicase. A carboxy fragment of the HCV NS3 protein was purified and possessed RNA helicase activity. Detections from the amino terminus resulted in the protein becoming soluble. Deletions from the carboxy terminus do not result in a loss of helicase activity until at least 50 amino acids are deleted. the helicase activity requires ATP and divalent cations such as Mg<2+> and Mn<2+>. The helicase activity was blocked by monoclonal antibody specific to the HCV NS3 protein.

Description: HCV NS3 PROTEIN FRAGMENTS HAVING HELICASE ACπVITY AND IMPROVED SOLUBILITY Technical Field This invention relates to the molecular biology and virology ofthe hepatitis C virus (HCV). More specifically, this invention relates to (1) carboxy terminus helicase fragments ofthe HCV NS3 protein having improved solubility in extraction and assay buffers, (2) methods of expressing the novel NS3 protein helicase fragments having improved solubility, (3) recombinant NS3 protein helicase fragments having improved solubility; (4) NS3 protein helicase mutant fragments; and (5) methods of using the HCV NS3 protein helicase fragments for screening helicase inhibitors as potential therapeutic agents. Background ofthe Invention Non- A, Non-B hepatitis (NANBH) is a transmissible disease (or family of diseases) that is believed to be virally induced, and is distinguishable from other forms of virus-associated liver disease, such as those caused by hepatitis A virus (HAV), hepatitis B virus (HBV), delta hepatitis virus (HDV), cytomegalovirus (CMV) or Epstein-Barr virus (EBV). Epidemiologic evidence suggests that there may be three types of NANBH: the water-borne epidemic type; the blood or needle associated type; and the sporadically occurring (community acquired) type. However, the number of causative agents is unknown. Recently, however, a new viral species, hepatitis C virus (HCV) has been identified as the primary (if not only) cause of blood-associated NANBH (BB-NANBH). See for example, PCT WO89/046699 and WO92/02642; European Patent Specification 318,216-B, and European Patent Application Publication Nos 388,232-A and 398,748- A, each incorporated herein by reference. Hepatitis C appears to be the major form of transfusion-associated hepatitis in a number of countries, including the United States and Japan. There is also evidence implicating HCV in induction of hepatocellular carcinoma. -4- Figure 3 shows the conserved sequence motif of DEXH box RNA helicase proteins and comparative alignment ofthe RNA helicase domain ofthe HCV NS3 protein. The numbers between boxes indicate the distance in amino acids residues. Figure 4 shows the structure of double strand RNA substrate for RNA helicase assay. The thick line indicates the 3 P-labeled RNA strand. The thin line indicates the unlabeled RNA strand. Figure 5 shows the expression and purification of HCV NS3 from E. Coli. M: protein size markers, Lane 1 : Total protein from uninduced cells, Lane 2: Total protein from 3 hr IPTG induced cells, Lane 3: HCV NS3:His-tag fusion protein purified by nickel binding chromatography. Figure 6 shows the results of an RNA helicase assay ofthe HCV NS3 protein fragments. Lane (-) enzyme: ds RNA without NS3 protein. Lane boiled: ds RNA denatured by heat. Lane 1 ; Fraction from negative control cell (pΕT vector only), Lane 2: 3 2+ 2+ 2+ mM Mn , Lane 3: no Mn , Lane 4: 3 mM Mg , Lane 5:no Mg 2+ , Lane 6:3 mM KCI , Lane 7:no ATP, Lane 8:1 mM ATP, Lane 9:preincubation ofthe NS3 protein with NS3- specific monoclonal antibody, Lanes 10, 11: preincubation ofthe NS3 protein with anticormexin monoclonal antibody at 0.5 μg, 1.0 μg per 20μl, respectively. Monoclonal antibodies were preincubated with the S3 protein at room temperature for 5 min. Figure 7 shows the activity profiles ofthe HCV NS3 RNA fragment having helicase activity with different ATP and divalent cations concentrations. The effects of cations were tested at two different ATP concentrations (1 mM and 5 mM). Figure 8 shows the activity of various truncated fragments ofthe HCV NS3 protein. showed that two thirds ofthe carboxy terminal fragment of HCV NS3 expressed in E. coli had polynucleotide-stimulated NTPase activity. J. Virol. 67:6152-6158 (1993). Gwack et al., in "NTPase Activity of Hepatitis C Virus NS3 Protein Expressed in Insect Cells" Mol. Cells. 5(2): 171-175 (1995), showed two HCV NS3 proteins, p70 and p43, were expressed in a baculovirus expression system. The p70 showed a specific NTPase activity that was inhibited by NS3 monoclonal antibodies. Warrener et al., "Pestivirus NS3 (p80) Protein Possesses RNA Helicase Activity," J. Virol. 69:1720-1726 (1995), demonstrated that bovine viral diarrhea virus (BVDV) NS3 protein expressed in a baculovirus expression system had a RNA helicase activity. JP 0631 9583A describes the preparation of a helicase protein encoded by HCV by introducing a HCV helicase gene into the non-essential region of a baculovirus. The helicase amino acid sequence is reported as 1200 through 1500 ofthe HCV polyprotein. All documents mentioned above are incorporated herein in their entirety by reference. Disclosure ofthe Invention We have now invented recombinant HCV NS3 protein fragments having helicase activity and improved solubility, fusion HCV NS3 protein fragments having helicase activity and improved solubility, truncated and altered HCV NS3 protein fragments having helicase activity and improved solubility, and cloning and expression vectors therefore, and methods for using these protein fragments in screening assays to assess whether a compound is capable of inhibiting RNA helicase activity and thus inhibiting HCV replication. Brief Description of he Drawings Figure 1 shows the sequence ofthe ofthe NS3 protein of HCV- 1, which is approximately from amino acid 1027 to 1657 ofthe HCV-1 polyprotein. (SEQ ID NO: 1) Figure 2 is a schematic presentation ofthe HCV NS3 protein. The numbers indicate the amino acid positions ofthe HCV-1 polyprotein. -6- Viruses: The Togaviridae And Flaviviridae" (Series eds. Fraenkel-Conrat and Wagner, vol. eds. Schlesinger and Schlesinger, Plenum Press, 1986), pp. 327-374. Generally, with respect to morphology, Flaviviruses contain a central nucleocapsid surrounded by a lipid bilayer. Virions are spherical and have a diameter of about 40-50 nm. Their cores are about 25-30 nm in diameter. Along the outer surface ofthe virion envelope are projections measuring about 5-10 nm in length with terminal knobs about 2 nm in diameter. Typical examples ofthe family include Yellow Fever virus, West Nile virus, and Dengue Fever virus. They possess positive-stranded RNA genomes (about 11,000 nucleotides) that are slightly larger than that of HCV and encode a polyprotein precursor of about 3500 amino acids. Individual viral proteins are cleaved from this precursor polypeptide. The genome of HCV appears to be single-stranded RNA containing about 10,000 nucleotides. The genome is positive-stranded, and possesses a continuous translational open reading frame (ORF) that encodes a polyprotein of about 3,000 amino acids. In the ORF, the structural proteins appear to be encoded in approximately the first quarter ofthe N-terminal region, with the majority ofthe polyprotein attributed to non¬ structural proteins. When compared with all known viral sequences, small but significant co-linear homologies are observed with the non-structural proteins ofthe Flavivirus family, and with the pestiviruses (which are now also considered to be part ofthe Flavivirus family). The HCV polyprotein is processed by the host and viral proteases during or after translation. The genetic map of HCV is as follows: from the amino terminus to the carboxy terminus, the nucleocapsid protein (C), the envelope proteins (El) and (E2), and the non-structural proteins 2, 3, 4 (a+b), and 5 (a+b) (NS2, NS3, NS4, and NS5). Based upon the putative amino acids encoded in the nucleotide sequence of HCV 1, a small domain at the extreme N-terminus ofthe HCV polyprotein appears similar both in size and high content of basic residues to the nucleocapsid protein (C) found at the N-terminus of flaviviral polyproteins. The non-structural proteins 2,3,4, and 5 (NS2-5) of HCV and of yellow fever virus (YFV) appear to have counterparts of similar size and hydropathicity, Figure 9 shows the various truncated HCV NS3 fragments and whether the fragments showed helicase/NTPase activity. Modes of Carrying Out The Invention A. Definitions The terms "Hepatitis C Virus" and "HCV" refer to the viral species that is the major etiological agent of BB-NANBH, the prototype isolate of which is identified in PCT WO89/046699; EPO publications 318,216, 388,232 and 398,748, and PCT WO92/02642. "HCV" as used herein includes the pathogenic strains capable of causing hepatitis C, and attenuated strains or defective interfering particles derived therefrom. The HCV genome is comprised of RNA. It is known that RNA-containing viruses have relatively high rates of spontaneous mutation, reportedly on the order of 10 -3 to 10 -4 per incorporated nucleotide (Fields & Knipe, "Fundamental Virology" (1986, Raven Press, N.Y.)). As heterogeneity and fluidity of genotype are inherent characteristics of RNA viruses, there will be multiple strains/isolates, which may be virulent or avirulent, within the HCV species. Information on several different strains/isolates of HCV is disclosed herein, particularly strain or isolate CDC/HCVI (also called HCVl). Information from one strain or isolate, such as a partial genomic sequence, is sufficient to allow those skilled in the art using standard techniques to isolate new strains/isolates and to identify whether such new strains/isolates are HCV. Typically, different strains, which may be obtained from a number of human sera (and from different geographical areas), are isolated utilizing the information from the genomic sequence of HCV 1. HCV is now classified as a new genus ofthe Flaviviridae family of which the other two genera are pestivirus and flavivirus. The Flavivirus family contains a large number of viruses which are small, enveloped pathogens of man. The moφhology and composition of Flavivirus particles are known, and are discussed in M.A. Brinton, in "The Val Asp Phe lie Pro Val Glu Asn Leu Glu Thr Thr Met Arg Ser Pro Val Phe Thr Asp Asn Ser Ser Pro Pro Val Val Pro Gin Ser Phe Gin Val Ala His Leu His Ala Pro Thr Gly Ser Gly Lys Ser Thr Lys Val Pro Ala Ala Tyr Ala Ala Gin Gly Tyr Lys Val Leu Val Leu Asn Pro Ser Val Ala Ala Thr Leu Gly Phe Gly Ala Tyr Met Ser Lys Ala His (Leu) Gly lie Asp Pro Asn lie Arg Thr Gly Val Arg Thr lie Thr Thr Gly Ser Pro lie Thr Tyr Ser Thr Tyr Gly Lys Phe Leu Ala Asp Gly Gly Cys Ser Gly Gly Ala Tyr Asp lie lie lie Cys Asp Glu Cys His Ser Thr Asp Ala Thr Ser He Leu Gly He Gly Thr Val Leu Asp Gin Ala Glu Thr Ala Gly Ala Arg Leu Val Val Leu Ala Thr Ala Thr Pro Pro Gly Ser Val Thr Val Pro His Pro Asn He Glu Glu Val Ala Leu Ser Thr Thr Gly Glu He Pro Phe Tyr Gly Lys Ala He Pro Leu Glu Val He Lys Gly Gly Arg His Leu He Phe Cys His Ser Lys Lys Lys Cys Asp Glu Leu Ala Ala Lys Leu Val Ala Leu Gly He Asn Ala Val Ala Tyr Tyr Arg Gly Leu Asp Val Ser Val He Pro Thr Ser Gly Asp Val Val Val Val Ala Thr A3p Ala Leu Met Thr Gly Tyr Thr Gly Asp Phe Asp Ser Val He (Tyr) Asp Cys Asn Thr Cys Val Thr Gin Thr Val (Ser) Asp Phe Ser Leu Asp Pro Thr Phe Thr He Glu Thr He Thr Leu Pro Gin Asp Ala Val Ser Arg Thr Gin Arg Arg Gly Arg Thr Gly Arg Gly Lys Pro Gly He Tyr Arg Phe Val Ala Pro Gly Glu Arg Pro Ser Gly Met Phe Asp Ser Ser Val Leu Cys Glu Cys Tyr Asp Ala Gly Cys Ala Trp Tyr Glu Leu Thr Pro Ala Glu Thr Thr Val Arg Leu Arg Ala Tyr Met Asn Thr Pro Gly Leu Pro Val Cys Gin Asp His Leu Glu Phe Trp Glu Gly Val Phe Thr Gly Leu Thr His He Asp Ala His Phe Leu Ser Gin Thr Lys Gin Ser Gly Glu Asn Leu Pro Tyr Leu Val Ala Tyr Gin Ala Thr although the amino acid sequences diverge. The region of HCV, which would correspond to the regions of YFV polyprotein that contains the M, E, and NSl protein, not only differs in sequence, but also appears to be quite different in size and hydropathicity. Thus, while certain domains ofthe HCV genome may be referred to herein as, for example, El , E2, or NS2, it should be understood that these designations are for convenience of reference only; there may be considerable differences between the HCV family and flaviviruses that have yet to be appreciated and as these differences surface, domain designations may change. Due to the evolutionary relationship ofthe strains or isolates of HCV, putative HCV strains and isolates are identifiable by their homology at the polypeptide level. With respect to the isolates disclosed herein, new HCV strains or isolates are expected to be at least about 40% homologous, some more than about 70% homologous, and some even more than about 80% homologous: some may be more than about 90% homologous at the polypeptide level. The techniques for deteπriining amino acid sequence homology are known in the art. For example, the amino acid sequence may be determined directly and compared to the sequences provided herein. Alternatively the nucleotide sequence ofthe genomic material ofthe putative HCV may be determined (usually via a cDNA intermediate), the amino acid sequence encoded therein can be determined, and the corresponding regions compared. The term "NS3 protein fragment showing helicase activity" or "NS3 protein helicase fragment" refers to an enzyme derived from an HCV NS3 protein which exhibits helicase activity, specifically the portion of polypeptide that is encoded in the carboxy two- third terminus ofthe NS3 domain ofthe HCV genome. Generally, the portion ofthe HCV NS3 protein showing protease activity, i.e., that which is found in the amino one-third terminus, has been removed. At least one strain of HCV contains a NS3 protein fragment showing helicase activity believed to be substantially encoded by or within the following sequence of amino acids residues within the NS3 protein fragment i.e.; approximately amino acids 1193 to 1657 ofthe NS3 protein shown in Figure 1. The sequence of such helicase fragment is depicted below: -10- purification and assay buffers. The NS3 protein generally is insoluble in buffers. When approximately 20 amino acids of helicase N terminus are deleted, the fragments become soluble in buffer. When approximately thirty-five amino acids are deleted, however, the fragments lose both NTPase and helicase activity. It is known that a portion ofthe NS3 protein at the amino terminus i.e., that beginning around amino acid 1027 exhibits protease activity. Protease activity, however, is not required ofthe HCV helicases ofthe invention and, in fact, the amino terminus fragments of NS3 exhibiting protease activity have been deleted from the helicase or fragments ofthe present invention. "HCV NS3 fragment helicase analogs" refer to polypeptides which vary from the NS3 carboxy fragment having helicase activity, shown above, by deletion, alter¬ ation and/or addition to the amino acid sequence ofthe native helicase fragment. HCV NS3 helicase fragment analogs include the truncated helicase fragments described above, as well as HCV NS3 fragment helicase mutants and fusion helicase fragments comprising HCV NS3 protein helicase fragments, truncated NS3 protein helicase fragments, or NS3 fragment helicase mutants. Alterations to form HCV NS3 fragment helicase mutants are preferably conservative amino acid substitutions, in which an amino acid is replaced with another naturally-occurring amino acid of similar character. For example, the following substitutions are considered "conservative": Gly « Ala; Asp « Glu; Val « He « Leu; Lys « Arg; Asn « Gin; and Phe « Tφ « Tyr. Nonconservative changes are generally substitutions of one ofthe above amino acids with an amino acid from a different group (e.g., substituting Asn for Glu), or substituting Cys, Met, His, or Pro for any ofthe above amino acids. Substitutions involving common amino acids are conveniently performed by site specific mutagenesis of an expression vector encoding the desired protein, and subsequent expression ofthe altered form. One may also alter amino acids by synthetic or semi-synthetic methods. For example, one may convert cysteine or serine residues to selenocysteine by appropriate chemical treatment ofthe isolated protein. Alternatively, one may incoφorate uncommon amino acids in standard in vitro protein synthetic methods. Typically, the total number of residues changed, deleted or Val Cys Ala Arg Ala Gin Ala Pro Pro Pro Ser Trp Asp Gin Met Trp Lys Cys Leu He Arg Leu Lys Pro Thr Leu His Gly Pro Thr Pro Leu Leu Tyr Arg Leu Gly Ala Val Gin Asn Glu He Thr Leu Thr His Pro Val Thr Lys Tyr He Met Thr Cys Met Ser Ala Asp Leu Glu Val Val Thr 1658 (SEQ ID NO: 2) The above N and C termini ofthe helicase fragment are putative, the actual termini being defined by expressing and processing in an appropriate host of a DNA construct encoding the entire NS3 domain. It is understood that this sequence may vary from strain to strain, as RNA viruses, like HCV, are known to exhibit a great deal of variation. Further, the actual N and C termini may vary, as the NS3 protein fragment showing helicase activity is cleaved from a precursor polyprotein: variations in the helicase amino acid sequence can result in different termini for helicase activity. Thus, the amino- and carboxy-termini may differ from strain to strain of HCV. A minimum sequence necessary for activity does exist and has been determined herein. The sequence ofthe NS3 fragment may be truncated at either end or at both by treating an appropriate expression vector with exonuclease after cleavage with a restriction endonuclease at the 5 ' or 3' end (or both) ofthe coding sequence to remove any desired number of base pairs. The resulting coding polynucleotide is then expressed and the sequence determined. In this manner the activity ofthe resulting product may be correlated with the amino acid sequence: a limited series of such experiments (removing progressively greater numbers of base pairs) determines the minimum internal sequence necessary for helicase activity. The sequence of the HCV NS3 fragment may be substantially truncated, particularly at the carboxy terminus up to approximately 50 amino acids, with full retention of helicase activity. Successive carboxy truncations do eventually result in the loss of helicase activity. Further carboxy truncation, at around 135 amino acids results in the loss of NTPase activity. The amino terminus ofthe NS3 fragment, i.e., that beginning around 1190 ofthe HCV-1 amino acid sequence may also be truncated to a degree without a loss of helicase activity. Suφrisingly, an amino terminus truncation to around twenty amino acids ofthe putative helicase domain does, however, result in an increase in the solubility ofthe fragment in -12- B. General Method The practice ofthe present invention generally employs conventional techniques of molecular biology, microbiology, recombinant DNA, and immunology, which are within the skill ofthe art. Such techniques are explained fully in the literature. See for example J. Sambrook et al, "Molecular Cloning; A Laboratory Manual (1989); "DNA Cloning", Vol. I and II (D.N Glover ed. 1985); "Oligonucleotide Synthesis" (MJ. Gait ed, 1984); "Nucleic Acid Hybridization" (B.D. Hames & S.J. Higgins eds. 1984); "Transcription And Translation" (B.D. Hames & S.J. Higgins eds. 1984); "Animal Cell Culture" (R.I. Freshney ed. 1986); "Immobilized Cells And Enzymes" (IRL Press, 1986); B. Perbal, "A Practical Guide To Molecular Cloning" (1984); the series, "Methods In Enzymology" (Academic Press, Inc.); "Gene Transfer Vectors For Mammalian Cells" (J.H. Miller and M.P. Calos eds. 1987, Cold Spring Harbor Laboratory); Meth Enzymol (1987) 154 and 155 (Wu and Grossman, and Wu, eds., respectively); Mayer & Walker, eds. (1987), "Immunochemical Methods In Cell And Molecular Biology" (Academic Press, London); Scopes, "Protein Purification: Principles And Practice", 2nd Ed (Springer- Verlag, N.Y., 1987); and "Handbook Of Experimental Immunology", volumes I-IV (Weir and Blackwell, eds, 1986). Both prokaryotic and eukaryotic host cells are useful for expressing desired coding sequences when appropriate control sequences compatible with the designated host are used. Among prokaryotic hosts, E. coli is most frequently used. Expression control sequences for prokaryotes include promoters, optionally containing operator portions, and ribosome binding sites. Transfer vectors compatible with prokaryotic hosts are commonly derived from, for example, pBR322, a plasmid containing operons conferring ampicillin and tetracycline resistance, and the various pUC vectors, which also contain sequences conferring antibiotic resistance markers. These plasmids are commercially available. The markers may be used to obtain successful transformants by selection. Commonly used prokaryotic control sequences include the T7 bacteriophage promoter (Dunn and Studier, Mol. Biol. (1983) 166:477) the b-lactamase (penicillinase) and lactose promoter systems (Chang et al, Nature ( 1977) 128: 1056), the tryptophan (tφ) promoter system (Goeddel et added to the native sequence in the mutants will be no more than about 20, preferably no more than about 10, and most preferably no more than about 5. The term fusion protein generally refers to a polypeptide comprising an amino acid sequence drawn from two or more individual proteins. In the present invention, "fusion protein" is used to denote a polypeptide comprising the HCV NS3 helicase fragment, truncate, mutant or a functional portion thereof, fused to a non-HCV protein or polypeptide ("fusion partner"). Fusion proteins are most conveniently produced by expressing of a fused gene, which encodes a portion of one polypeptide at the 5' end and a portion of a different polypeptide at the 3' end, where the different portions are joined in one reading frame which may be expressed in a suitable host. It is presently preferred (although not required) to position the HCV NS3 helicase fragment or analog at the car¬ boxy terminus ofthe fusion protein, and to employ a functional enzyme fragment at the amino terminus. The HCV NS3 helicase fragment is normally expressed within a large polyprotein. The helicase fragment is not expected to include cell transport signals (e.g., export or secretion signals). Suitable functional enzyme fragments are those polypeptides which exhibit a quantifiable activity when expressed fused to the HCV NS3 helicase fragment. Exemplary enzymes include, without limitation, b-galactosidase (b-gal), b-lac- tamase, horseradish peroxidase (HRP), glucose oxidase (GO), human superoxide dismutase (hSOD), urease, and the like. These enzymes are convenient because the amount of fusion protein produced can be quantified by means of simple colorimetric assays. Alternatively, one may employ fragments or antigenic proteins, to permit simple detection by metal- binding columns and quantification of fusion proteins using antibodies specific for the fusion partner. The presently preferred fusion partner is six histidine residues at the carboxy terminus. -14- amino acid polypeptide which is automatically cleaved from the fused protein upon expression. The ubiquitin amino acid sequence is as follows: Gin He Phe Val Lys Thr Leu Thr Gly Lys Thr He Thr Leu Glu Val Glu Ser Ser Asp Thr He Asp Asn Val Lys Ser Lys He Gin Asp Lys Glu Gly He Pro Pro Asp Gin Gin Arg Leu He Phe Ala Gly Lys Gin Leu Glu Asp Gly Arg Thr Leu Ser Asp Tyr Asn He Gin Lys Glu Ser Thr Leu His Leu Val Leu Arg Leu Arg Gly Gly (SEQ ID NO: 3) See also Ozkaynak et al, Nature (1984) 112:663-66. Polynucleotides encoding the ubiquitin polypeptide may be synthesized by standard methods, for example following the technique of Barr et al, J Biol Chem (1988) 2££: 1671-78 using an Applied Biosystem 380A DNA synthesizer. Using appropriate linkers, the ubiquitin gene may be inserted into a suitable vector and ligated to a sequence encoding the HCV helicase or a fragment thereof. In addition, the transeriptional regulatory region and the transeriptional initiation region which are operably linked may be such that they are not naturally associated in the wild-type organism. These systems are described in detail in EPO 120,551, published October 3, 1984; EPO 116,201, published August 22, 1984; and EPO 164,556, published December 18, 1985, all of which are commonly owned with the present invention, and are hereby incoφorated herein by reference in full. Mammalian cell lines available as hosts for expression are known in the art and include many immortalized cell lines available from the American Type Culture Collection (ATCC), including HeLa cells, Chinese hamster ovary (CHO) cells, baby hamster kidney (BHK) cells, and a number of other cell lines. Suitable promoters for mam¬ malian cells are also known in the art and include viral promoters such as that from Simian Virus 40 (SV40) (Fiers et al, Nature (1978) 222: 113), Rous sarcoma virus (RSV), adeno¬ virus (ADV), and bovine papilloma virus (BPV). Mammalian cells may also require terminator sequences and poly-A addition sequences. Enhancer sequences which increase expression may also be included, and sequences which promote amplification ofthe gene al, Nuc Acids Res (1980) 8_:4057) and the lambda-derived P j promoter and N gene ribosome binding site (Shimatake et al, Nature (1981) 222:128) and the hybrid tac promoter (De Boer et al, Proc Nat Acad Sci USA (1983) 222:128) derived from sequences ofthe li and laς UV5 promoters. The foregoing systems are particularly compatible with E. coli; if desired, other prokaryotic hosts such as strains of Bacillus or Pseudomonas may be used, with corresponding control sequences. Eukaryotic hosts include, without limitation, yeast and mammalian cells in culture systems. Yeast expression hosts include Saccharomyces, Klebsiella, Pichia. and the like. Saccharomyces cerevisiae and Saccharomyces carlsbergensis and K. lactis are the most commonly used yeast hosts, and are convenient fungal hosts. Yeast-compatible vectors carry markers which permit selection of successful transformants by conferring prototrophy to auxotrophic mutants or resistance to heavy metals on wild-type strains. Yeast compatible vectors may employ the 2m origin of replication (Broach et al, Meth Enzymol (1983) 101:307), the combination of CEN3 and ARS1 or other means for assuring replication, such as sequences which will result in incoφoration of an appropriate fragment into the host cell genome. Control sequences for yeast vectors are known in the art and include promoters for the synthesis of glycolytic enzymes (Hess et al, J Adv Enzvme Reg (1968) 2:149; Holland et al, Biochem (1978), 12:4900), including the promoter for 3 -phosphoglycerate kinase (R. Hitzeman et al, J Biol Chem (1980) 255:2073). Terminators may also be included, such as those derived from the enolase gene (Holland, J Biol Chem (1981) 256:1385). Particularly useful control systems are those which comprise the glyceraldehyde-3 phosphate dehydrogenase (GAPDH) promoter or alcohol dehydrog¬ enase (ADH) regulatable promoter, terminators also derived from GAPDH, and if secretion is desired, a leader sequence derived from yeast a-factor (see U.S. Pat. No. 4,870,008, incoφorated herein by reference). A presently preferred expression system employs the ubiquitin leader as the fusion partner. Copending application USSN 7/390,599 filed 7 August 1989 disclosed vec- tors for high expression of yeast ubiquitin fusion proteins. Yeast ubiquitin provides a 76 -16- use the strong viral polyhedrin gene promoter to drive expression of heterologous genes. Currently the most commonly used transfer vector for introducing foreign genes into AcNPV is pAc373 (see PCT WO89/046699 and USSN 7/456,637). Many other vectors known to those of skill in the art have also been designed for improved expression. These include, for example, pVL985 (which alters the polyhedrin start codon from ATG to ATT, and introduces a BamHI cloning site 32 bp downstream from the ATT; See Luckow and Summers, Virol (1989) 12:31 ). AcNPV transfer vectors for high level expression of nonfused foreign proteins are described in copending applications PCT WO89/046699 and USSN 7/456,637. A unique BamHI site is located following position -8 with respect to the translation initiation codon ATG ofthe polyhedrin gene. There are no cleavage sites for Smal, PstI, Bglll, Xbal or SstI. Good expression of nonfused foreign proteins usually requires foreign genes that ideally have a short leader sequence containing suitable translation initiation signals preceding an ATG start signal. The plasmid also contains the polyhedrin polyadenylation signal and the ampicillin-resistance (amp) gene and origin of replication for selection and propagation in E. coli. Methods for the introduction of heterologous DNA into the desired site in the baculovirus virus are known in the art. (See Summer and Smith, Texas Agricultural Experiment Station Bulletin No. 1555; Smith et al, Mol Cell Biol (1983) 2:2156-2165; and Luckow and Summers. Virol (1989) 17:31). For example, the heterologous DNA can be inserted into a gene such as the polyhedrin gene by homologous recombination, or into a restriction enzyme site engineered into the desired baculovirus gene. The inserted sequences may be those that encode all or varying segments ofthe polyprotein, or other orfs that encode viral polypeptides. For example, the insert could encode the following numbers of amino acid segments from the polyprotein: amino acids 1-1078; amino acids 332-662; amino acids 406-662; amino acids 156-328, and amino acids 199-328. The signals for post-translational modifications, such as signal peptide cleavage, proteolytic cleavage, and phosphorylation, appear to be recognized by insect cells. The signals required for secretion and nuclear accumulation also appear to be may also be desirable (for example methotrexate resistance genes). These sequences are known in the art. Vectors suitable for replication in mammalian cells are known in the art, and may include viral replicons, or sequences which insure integration ofthe appropriate sequences encoding HCV epitopes into the host genome. For example, another vector used to express foreign DNA is Vaccinia virus. In this case the heterologous DNA is inserted into the Vaccinia genome. Techniques for the insertion of foreign DNA into the vaccinia virus genome are known in the art, and may utilize, for example, homologous recombina- tion. The heterologous DNA is generally inserted into a gene which is non-essential to the virus, for example, the thymidine kinase gene (Ik), which also provides a selectable marker. Plasmid vectors that greatly facilitate the construction of recombinant viruses have been described (see, for example, Mackett et al, J Virol (1984) 42:857; Chakrabarti et al, Mol Cell Biol (1985) 5:3403; Moss, in GENE TRANSFER VECTORS FOR MAMMALIAN CELLS (Miller and Calos, eds., Cold Spring Harbor Laboratory, NY, 1987), p. 10). Expression ofthe HCV polypeptide then occurs in cells or animals which are infected with the live recombinant vaccinia virus. In order to detect whether or not the HCV polypeptide is expressed from the vaccinia vector, BSC 1 cells may be infected with the recombinant vector and grown on microscope slides under conditions which allow expression. The cells may then be acetone-fixed, and immunofluorescence assays performed using serum which is known to contain anti-HCV antibodies to a polypeptide(s) encoded in the region ofthe HCV genome from which the HCV segment in the recombinant expression vector was derived. Other systems for expression of eukaryotic or viral genomes include insect cells and vectors suitable for use in these cells. These systems are known in the art, and include, for example, insect expression transfer vectors derived from the baculovirus Autographa califomica nuclear polyhedrosis virus (AcNPV), which is a helper- independent, viral expression vector. Expression vectors derived from this system usually -18- Sticky-ended cleavage fragments may be blunt ended using E. coli DNA polymerase I (Klenow fragment) with the appropriate deoxynucleotide triphosphates (dNTPs) present in the mixture. Treatment with Sl nuclease may also be used, resulting in the hydrolysis of any single stranded DNA portions. Ligations are carried out under standard buffer and temperature conditions using T4 DNA ligase and ATP; sticky end ligations require less ATP and less ligase than blunt end ligations. When vector fragments are used as part of a ligation mixture, the vector fragment is often treated with bacterial alkaline phosphatase (BAP) or calf intestinal alkaline phosphatase to remove the 5'-phosphate, thus preventing religation ofthe vector. Alternatively, restriction enzyme digestion of unwanted fragments can be used to prevent ligation. Ligation mixtures are transformed into suitable cloning hosts, such as E. coli, and successful transformants selected using the markers incorporated (e.g., antibiotic resistance), and screened for the correct construction. Synthetic oiigonucleotides may be prepared using an automated oligo- nucleotide synthesizer as described by Warner, DNA ( 1984) 2:401. If desired, the synthetic strands may be labeled with P by treatment with polynucleotide kinase in the presence of 32 P-ATP under standard reaction conditions. DNA sequences, including those isolated from cDNA libraries, may be modified by known techniques, for example by site directed mutagenesis (see e.g., Zoller, Nuc Acids Res (1982) 1Q_:6487). Briefly, the DNA to be modified is packaged into phage as a single stranded sequence, and converted to a double stranded DNA with DNA polymerase, using as a primer a synthetic oligonucleotide complementary to the portion of the DNA to be modified, where the desired modification is included in the primer sequence. The resulting double stranded DNA is transformed into a phage-supporting host conserved between the invertebrate cells and vertebrate cells. Examples ofthe signal sequences from vertebrate cells which are effective in invertebrate cells are known in the art, for example, the human interleukin-2 signal (IL2 ) which signals for secretion from the cell, is recognized and properly removed in insect cells. Transformation may be by any known method for introducing polynuc¬ leotides into a host cell, including, for example packaging the polynucleotide in a virus and transducing a host cell with the virus, and by direct uptake ofthe polynucleotide. The transformation procedure used depends upon the host to be transformed. Bacterial transfor- mation by direct uptake generally employs treatment with calcium or rubidium chloride (Cohen, Proc Nat Acad Sci USA (1972) 62:2110; T. Maniatis et al, "Molecular Cloning; A Laboratory Manual" (Cold Spring Harbor Press, Cold Spring Harbor, NY, 1982). Yeast transformation by direct uptake may be carried out using the method of Hinnen et al, Proc Nat Acad Sci USA (1978) 25: 1929. Mammalian transformations by direct uptake may be conducted using the calcium phosphate precipitation method of Graham and Van der Eb, Virol (1978) 52:546, or the various known modifications thereof. Other methods for introducing recombinant polynucleotides into cells, particularly into mammalian cells, include dextran-mediated transfection, calcium phosphate mediated transfection, polybrene mediated transfection, protoplast fusion, electroporation, encapsulation ofthe polynucleo- tide(s) in liposomes, and direct microinjection ofthe polynucleotides into nuclei. Vector construction employs techniques which are known in the art. Site- specific DNA cleavage is performed by treating with suitable restriction enzymes under conditions which generally are specified by the manufacturer of these commercially available enzymes. In general, about 1 mg of plasmid or DNA sequence is cleaved by 1 unit of enzyme in about 20 mL buffer solution by incubation for 1-2 hr at 37°C. After incubation with the restriction enzyme, protein is removed by phenol/chloroform extraction and the DNA recovered by precipitation with ethanol. The cleaved fragments may be separated using polyacrylamide or agarose gel electrophoresis techniques, according to the general procedures described in Meth Enzymol (1980) 65:499-560. -20- following chloramphenicol amplification (Clewell, J Bacteriol (1972) HQ:667). The DNA is isolated and analyzed, usually by restriction enzyme analysis and/or sequencing. Sequencing may be performed by the dideoxy method of Sanger et al, Proc Nat Acad Sci USA (1977) 24:5463, as further described by Messing et al, Nuc Acids Res (1981) 2:309, or by the method of Maxam et al, Meth Enzymol ( 1980) 65:499. Problems with band compression, which are sometimes observed in GC-rich regions, were overcome by use of T-deazoguanosine according to Barr et al, Biotechniques (1986) 4:428. The enzyme-linked immunosorbent assay (ELISA) can be used to measure either antigen or antibody concentrations. This method depends upon conjugation of an enzyme to either an antigen or an antibody, and uses the bound enzyme activity as a quantitative label. To measure antibody, the known antigen is fixed to a solid phase (e.g., a microtiter dish, plastic cup, dipstick, plastic bead, or the like), incubated with test serum dilutions, washed, incubated with anti-immunoglobulin labeled with an enzyme, and washed again. Enzymes suitable for labeling are known in the art, and include, for example, horseradish peroxidase (HRP). Enzyme activity bound to the solid phase is usually measured by adding a specific substrate, and determining product formation or substrate utilization colorimerrically. The enzyme activity bound is a direct function ofthe amount of antibody bound. To measure antigen, a known specific antibody is fixed to the solid phase, the test material containing antigen is added, after an incubation the solid phase is washed, and a second enzyme-labeled antibody is added. After washing, substrate is added, and enzyme activity is measured colorimetrically, and related to antigen concentration. The NS3 proteins ofthe three genera of Flaviviridae: flavivirus, pestivirus and HCV, have conserved sequence motifs of serine type proteinase and of nucleoside triphosphatase (NTPase)/RNA helicase. See Figure 2. The NTPase/RNA helicase carboxy two-thirds ofthe NS3 protein fragment belongs to the DEAD box family. The DEAD box protein family has eight highly conserved amino acid motifs, one of which is the DEAD bacterium. Cultures ofthe transformed bacteria which contain copies of each strand ofthe phage are plated in agar to obtain plaques. Theoretically, 50% ofthe new plaques contain phage having the mutated sequence, and the remaining 50% have the original sequence. Replicates ofthe plaques are hybridized to labeled synthetic probe at temperatures and conditions which permit hybridization with the correct strand, but not with the unmodified sequence. The sequences which have been identified by hybridization are recovered and cloned. DNA libraries may be probed using the procedure of Grunstein and Hogness Proc Nat Acad Sci USA (1975) 22:3961. Briefly, in this procedure the DNA to be probed is immobilized on nitrocellulose filters, denatured, and prehybridized with a buffer containing 0-50% formamide, 0.75 M NaCl, 75 mM Na citrate, 0.02% (wt/v) each of bovine serum albumin, polyvinylpyrrolidone, and Ficoll®, 50 mM NaH2PO4 (pH 6.5), 0.1% SDS, and 100 mg/mL carrier denatured DNA. The percentage of formamide in the buffer, as well as the time and temperature conditions ofthe prehybridization and subsequent hybridization steps depend on the stringency required. Oligomeric probes which require lower stringency conditions are generally used with low percentages of formamide, lower temperatures, and longer hybridization times. Probes containing more than 30 or 40 nucleotides, such as those derived from cDNA or genomic sequences generally employ higher temperatures, e.g., about 40-42°C, and a high percentage formam¬ ide, e.g., 50%. Following prehybridization, 5'- 32 P-labeled oligonucleotide probe is added to the buffer, and the filters are incubated in this mixture under hybridization conditions. After washing, the treated filters are subjected to autoradiography to show the location of the hybridized probe; DNA in corresponding locations on the original agar plates is used as the source ofthe desired DNA. For routine vector constructions, ligation mixtures are transformed into E. coli strain HB 101 or other suitable hosts, and successful transformants selected by anti¬ biotic resistance or other markers. Plasmids from the transformants are then prepared according to the method of Clewell et al, Proc Nat Acad Sci USA (1969) 62: 1159, usually -22- was inhibited by a NS3-specific monoclonal antibody, but, an unrelated antibody did not affect the activity. From these results, it was determined that the helicase activity was derived not from E. coli contaminants, but from the HCV NS3 protein fragments. Most ofthe investigated RNA helicases bound to single strand region and then unwound double strand RNA by moving unidirectionaly or bidirectionaly. The substrate with the single strand region on both 3' and 5' ends was used. Suzich et al, Virol.. 67:6152-6158 (1993) showed that the two thirds ofthe C'-terminal of HCV NS3 could hydrolyze all NTPs and dNTPs. This NTPase activity was observed with the HCV NS3 protein fragments disclosed herein. (data not shown) The results showing that the truncated NS3 protein fragments described herein having biochemical helicase activity in spite of deleted N -terminal proteinase domain suggest that the proteinase and NTPase domains may act independently. The HCV NS3 protein fragments showing helicase activity ofthe present invention are advantageous because they are soluble in purification and assay buffers, while the entire NS3 protein generally is not. The solubility ofthe helicase fragments was determined by first constructing several clones from various vectors and fusion proteins. For example, a pGΕX-2T vector containing a glutathione-s-transferase (GST) fusion protein was used to clone the HCV NS3 protein i.e., from 1027 to 1657 a.a. of HCV- 1. The resulting fusion protein of GST and HCV NS3 protein was insoluble, i.e., the only portion ofthe fusion protein that was isolated was that from the insoluble portion ofthe bacterial extract. That fusion protein was solubilized by denaturing with 6 M urea. When the denatured fusion protein was refolded by serial dialysis against a concentration step gradient, only a small fraction ofthe renatured fusion protein was correctly refolded and no enzymatic activity was observed in the renatured protein. When an HCV NS3 protein was fused with a maltose binding protein using a pMAL vector, the fusion protein was soluble. The molecular weight ofthe fusion protein, however, was relatively large (M.W. 110 kDa) because the maltose binding protein itself is about 40 kDa. Thus, such a fusion protein is undesirable to use. In addition, it is difficult to separate the maltose binding protein domain region where it is also known as an ATPase motif. The DEAD protein family consists of three subfamilies: DEAD proteins, DEAH proteins and DEXH proteins. Figure 3 shows the conserved sequence motifs of DEXH protein family and the corresponding motifs of HCV NS3. The HCV NS3 protein has sequence motif of DECH which results in its classification in the DEXH protein subfamily. The HCV NS3 protein fragments disclosed herein have similar characteristics with other known RNA helicases, i.e., they show RNA helicase activity only in the presence of divalent cations (Mn 2+ or Mg 2+ ) and ATP. At a lower level of ATP, (approximately 1 mM) an increasing amount of either cation inhibits the enzymatic activity ofthe NS3 fragment. When the ATP concentration is high, (approximately 5 mM), helicase activity remains at a high level even when Mg or Mn cations are present at high concentrations. RNA helicase A purified from HeLa cells, needs only Mg for its cofactor, and Mn does not substituted for Mg . See Lee et al., J. Biol. 267:4398-4407 (1992), incoφorated herein by reference. Pestivirus NS3 and Vaccinia virus RNA helicase have shown to use both cations. Likewise, HCV NS3 protein helicase fragments disclosed herein can utilize both metal ions. The helicase activity ofthe HCV NS3 protein helicase fragments is likely pH specific. The experiments in the examples were carried out at pH 6.5. When the pH was increased to 7.6, however, HCV NS3 protein helicase fragments showed not more than 10% strand separation, keeping all other components constant, (data not shown) These characteristics of HCV NS3 protein helicase fragments imply that it has a similar nature to pestivirus NS3 RNA helicase, which is known to pH sensitive. RNA helicase activity was confirmed not to be derived from E. coli contaminants in two ways. First, a pΕT21b plasmid without a HCV NS3 protein fragment insert was used as a negative control. The enzymatic activity ofthe same eluted fraction from the negative control cell culture was tested and there was no detectable level of NTPase or RNA helicase activity. Second, the NS3 protein fragment's helicase activity -24- polyacrylamide gel by studying the unwinding activity ofthe helicase fragment. The screening assay can also be automated in a microtiter dish (96-well plate) format. In the latter assay, the double-stranded template RNA is labeled with biotin at the 5 '-end of one strand and with P at the 5'-end ofthe other strand. This labeled template can be attached to the bottom ofthe well that is coated with streptavidin. The helicase activity from the added fragments can be measured by counting radioactivity from the displaced 32 P-labeled RNA strand that is now present in the well supernatant. Potential helicase inhibitors present in the combinatorial library can be found by detecting specific inhibition ofthe strand displacement reaction by helicase fragments. 10 C. Examples The examples presented below are provided as a further guide to the practitioner of ordinary skill in the art, and are not to be construed as limiting the invention in any way. 15 Example 1 Expression and purification of HCV NS3 protein. For expressing the carboxy two-thirds of HCV NS3 protein, the polymerase chain reaction (PCR) was used to amplify a 1.4 Kb 20 DNA fragment encompassing amino acids 1 193 to 1657 from HCV-1 cDNA. The sense primer used was JCK-1 5'-GGGGATCCGGTGGACTTTATCCCT-3' (SEQ ID NO: 4), and the antisense primer JCK-7 5'-GGAAGCTTGCTGACGACCTCG-3' (SEQ ID NO: 5). The PCR produced was digested with BamHI and Hindlll inserted into BamHI and Hindlll sites of pET21b (purchased from Novagen. WI). The recombinant plasmid was 25 designated as pET21b-NS3HCV and transformed to E. coli BL21 (DE3), and the inserted region was verified by sequencing. pET21b-NS3HCV consisted of 466 amino acid 1 As a negative control, a pET21b plasmid without the insert was transformed to E. coli BL21 (DΕ3) and induced with 1 mM IPTG. The negative control cell culture was processed with the same purification step as pET21b-NS3HCV. The negative control showed no enzymatic activity. See Figure 6, lane 1. out from the fusion protein containing it and the HCV NS3 protein. In addition, a pET21b vector was utilized to express the domain of HCV NS3 protein, amino acids 1027 to 1657. The expression level ofthe protein was very low and only a small quantity ofthe protein was isolated. Thus, the HCV NS3 protein fragments ofthe present invention in, e.g., a pET vector system, provides the following advantages: 1 ) a better T7 promoter system when compared to the promoters of pMAL or pGEX vector; 2) an increase in solubility ofthe expressed NS3 protein fragment having helicase activity; 3) an elimination ofthe necessity to remove the non-HCV NS3 protein fragment from the fusion protein; and 4) a convenient purification step by using nickel column chromatography. Further, a soluble NS3 protein fragment having helicase activity has several advantages to the insoluble full lentgth protein. First, it is not necessary for the soluble protein fragments to denature and refold for use in purification and enzyme assays. An insoluble protein or fragment needs to be denatured by urea or Guanidium-HCl for purification and then must be dialyzed against a concentration step gradient for removing the urea or Guanidium-HCl before refolding and recovery ofthe enzymatic activity ofthe protein fragment. Second, the yield of soluble NS3 protein fragments from expression systems is higher than that of insoluble NS3 protein fragments. During the denaturation-refolding process, an insoluble protein fragment is lost in a large portion ofthe cell extract. Third, the enzymatic activity ofthe insoluble NS3 proteins cannot be observed after refolding. Soluble helicase fragments of a HCV NS3 protein can be used to screen for specific helicase inhibitors from a combinatorial library. The screening assay can be performed based on the mobility shift ofthe double stranded template RNA in a -26- was labeled with [α- 32 P]-CTP, and the specific activity of labeled substrated was 1 - 1.5 x 10 cpm/pmol ds RNA substrate. Duplex RNA was eiectrophoresed on 6% native polyacrylamide gel (30:0.8), and the location ofthe ds RNA was identified by autoradiography. To recover the RNA substrate, a sliced gel fragment was ground in 400 μl of elution buffer (0.5 M annomium acetate, 0.1% SDS, 10 mM EDTA) and shaked vigorously at 4°C for 2 hrs. The supematants were extracted with chloroform and precipitated with ethanol, and the RNA pellet was dissolved in D.W. Example 3 RNA helicase assay. An RNA helicase assay was performed in 20 μl of reaction mixture: 1 pmol NS3 HCV protein fragment, 0.5 pmol ds RNA substrate, 25 mM MOPS-KOH (pH 6.5), 5mM ATP, 3 mM MnCl 2 , 2 mM DTT, 100 μg/ml BSA, and 2.5 U RNasin (Promega). The reaction mixture was incubated at 37°C for 30 min. The reaction was stopped by adding 5 μl of 5 x termination buffer [0.1 M Tris-Cl (pH 7.4), 20 mM EDTA, 0.5% SDS, 0.1% NP-40, 0.1% bromophenol blue, 0.1% xylene cyanol, and 50% glycerol]. Each aliquot was loaded on 6% native polyacrylamide gel (30:0.8) and eiectrophoresed at 80 V for 3 hr. The ds RNA substrate and unwound RNA strand were visualized by autoradiography. The effect of ATP and divalent metal ion on the NS3 protein fragment's helicase activity was investigated by carrying out the same reactions with 1 , 2, 3, 4, and 6 2+ 2+ mM Mn or Mg in the presence of 1 mM or 5 mM ATP. Strand separation efficiencies were calculated by counting the radioactivities ofthe bands with Phospholmager (Molecular Dynamics, Sunnyvale, CA). See Fig. 7 for the activity change ofthe HCV NS3 protein fragments at various concentrations of ATP and the divalent cations. The HCV + 2+ NS3 RNA helicase fragments required divalent ions such as Mg and Mn (See Fig. 6, lane 2 to 5). Strand displacement was observed only when Mg + or Mn + ions were present (See Fig. 6, lanes 2 and 4). When either these divalent cations or ATP was deleted, ds RNA was not unwound (See Fig. 6, lanes 3, 5, and 7). Monovalent potassium ion did Strand displacement were observed by band shift of the radiolabeled long strand. residues from the carboxy terminus of HCV NS3 and contained His-Tag (6 histidines) and 19 additional residues from the pET expression vector at C-terminal end for easier purification. About 54 kDa (481 amino acid residues) of HCV NS3 His-tag fusion protein was induced by 1 mM IPTG from E. coli BL21 (DE3) harboring the recombinant plasmid 5 to exponentially grow cells in LB medium with 10 mg/ml of ampicillin. (See Fig. 5, lanes 1 and 2). From 200 ml ofthe culture, 400 mg of protein of approximately 95% purity was obtained. After 3 hrs of culturing at 37°C, the cells were harvested and disrupted. Soluble parts of cell extract were loaded onto a metal-binding column. Resin-bound protein was eluted with 1 M imidazole, 0.5 M NaCl, 20 mM Tris-Cl pH 7.9. Eluted fractions were 10 subjected to SDS-PAGE, and protein-containing fractions were pooled and dialyzed against 50 mM Tris-Cl pH 7.9 for 4 hrs. The NTPase assay on polyethyleneimine cellulose TLC (J.T.Baker) was performed as previously described in Suzich et al , to confirm that final purified protein had active conformation. The purified protein showed an NTPase activity (data not shown). 15 Example 2 Preparation of substrate for RNA Helicase. Fig. 4 shows the structure ofthe double strand RNA used as a substrate of an RNA helicase. The long strand was prepared by in vitro 20 transcription of pGEMl that had been cleaved with Pvull, and the short strand was transcribed from the BamHI digested pSP65. Both strands were transcribed with SP6 RNA polymerase (New England Biolabs) according to the manufacturer's manual. After the transcription reaction, each aliquot was treated with RNase-free DNase (Promega) and extracted with phenolxhloroform, and precipitated with ethanol. Each RNA strand was 25 resuspended with 25 ml of hybridization buffer (20 mM HEPES-KOH pH 7.6, 0.5 M NaCl, 1 mM EDTA, 0.1% SDS), and mixed. The mixture was heated to 100°C for 5 min. and incubated at 65°C for 30 min. and incubated at 25°C overnight. The long strand RNA (One or more protein bands about 50 kDa appeared by IPTG induction, but only the 54 kDA NS3-His fusion protein was purified from the metal binding affinity column. (See Fig. 5, lane 3) -28- NS3 helicase domain , i.e., amino acid 1193 to amino acid 1608 ofthe HCV NS3 domain. ATCC deposit no. 97309; No. 5, an HCV HS3 fragment having 97 amino acids deleted from the C-terminus ofthe HCV NS3 helicase domain, i.e., amino acid 1193 to amino acid 1651 ofthe HCV NS3 domain, ATCC deposit no. 97310; No. 6, an HCV NS3 fragment having 135 amino acids deleted from the C-terminus ofthe HCV NS3 helicase domain, i.e., amino acid 1209 to amino acid 1657 ofthe HCV NS3 domain, ATCC deposit no. 97311; No. 7, an HCV NS3 fragment having 16 amino acids deleted from the N-terminus ofthe HCV NS3 helicase domain, i.e., from amino acid 1209 to amino acid 1657 ofthe HCV NS3 domain, ATCC deposit no. 97312; and No. 8, an HCV NS3 fragment having 32 amino acids deleted from the N-terminus ofthe HCV NS3 helicase domain, i.e., from amino acid 1225 to amino acid 1657 ofthe HCV NS3 domain, ATCC deposit no. 97313 As shown in Fig 9, truncated mutants, numbers 5, 6, and 8 mutants did not demonstrate RNA helicase activity. Mutant 7, however, did demonstrate NTPase activity even though its activity was about half of No. 1 (full length) protein. Fig. 8 shows the RNA helicase assay of truncated mutants. The upper band indicates dsRNA and the lower band ssRNA labelled with P. Boiled RNA indicates denatured dsRNA after boiling for 5 min, and was therefore a control for ssRNA. As shown in both Figs 8 and 9, truncated fragments numbers 5, 6, and 8 lost RNA helicase activity. Example 5 Determining solubility ofthe HCV NS3 fragments The solubility ofthe expressed protein from pET21b-HCVNS3 vector was determined by the following method: ITPG- induced cells were harvested at 6000 G for 5 mins. The cells were then resuspended with IX binding buffer (5 mM imidazole, 500 mM NaCl, 20 mM Tris-Cl pH 7.9). The resuspended cells were then frozen in a dry ice-ethanol bath and thawed on ice and sonicated for 2 min. Cell extracts were centrifuged at 27000 G for 30 min. The soluble part ofthe cell extract, the supematent and the insoluble part ofthe cell extract, the pellet, were subjected on SDS-PAGE. When a westem blot was carried out for the SDS- not activate the HCV NS3 protein fragment's helicase activity at these conditions (See Figure 6, lane 6). At 1 mM ATP, the helicase activity was lower than at 5mM (See Figure 6, lane 8). Enzymatic activity of NS3 was inhibited by monoclonal antibodies of HCV NS3 protein fragments (See Figure 6, lane 9), and was not blocked by a non-specific antibody at two different concentrations (See Figure 6, lanes 10 and 11). As mentioned above, RNA helicase activity ofthe HCV NS3 protein fragments was dependent on divalent cations and ATP. At low concentration of ATP (1 mM), helicase activity of NS3 was highest at a low concentration of either ofthe divalent cations, and, the helicase activity decreased when the concentration ofthe cations was increased. At high concentration of ATP (5 mM), most ofthe substrates were unwound at all ofthe tested cation concentrations. At 3 mM or 4 mM of cation concentration, either 2+ 2+ • Mn or Mg , the helicase activity was the highest. Thus, the helicase activity appears more sensitive to the divalent cation concentration in lower concentrations of ATP. In addition, the HCV NS3 protein fragments showed a slight bias for Mg 2+ . Example 4 Testing of Truncated HCV NS3 Fragments for Helicase Activity HCV NS3 fragments of varying sizes were expressed and purified as described above. The fragments were then tested for helicase activity as described above, and for NTPase activity as is known in the art. Fig. 9 depicts the fragments tested and whether the fragments showed helicase/NTPase activity. The following fragments were tested: No. 1, a full length helicase fragment, i.e., from amino acid 1193 to amino acid 1657 ofthe HCV NS3 domain, ATCC deposit no.97306; No. 2, an HCV NS3 fragment having 10 amino acids deleted from the C- terminus ofthe HCV NS3 helicase domain, i.e., from amino acid 1193 to amino acid 1648 ofthe HCV NS3 domain, ATCC deposit no. 97307; No. 3, an HCV NS3 fragment having 30 amino acids deleted from the C-terminus ofthe HCV NS3 helicase domain, i.e., amino acid 1193 to amino acid 1638 ofthe HCV NS3 domain, ATCC deposit no. 97308; No. 4, an HCV NS3 fragment having 50 amino acids deleted from the C-terminus ofthe HCV -30- WHAT IS CLAIMED IS: 1. A composition comprising an HCV NS3 helicase fragment having substantially the same amino acid sequence as shown in SEQ ID NO:2. 2. The composition of claim 1 wherein said fragment is produced by chemical synthesis or recombinant DNA expression. 3. A composition according to either of claims 1 or 2 wherein said fragment has its carboxy terminus at amino acid 1561 to 1657. 4. A composition according to any of claims 1-3, wherein said fragment has its amino acid terminus at amino acid 1193 to amino acid 1223. 5. A fusion protein comprising a suitable fusion partner fused to a HCV NS3 helicase fragment having substantially the amino acid sequence as shown in SEQ ID NO:2. 6. The fusion protein of claim 5 wherein said fusion partner comprises human superoxide dismutase. 7. The fusion protein according to either of claims 5 or 6 wherein said fragment is produced by chemical synthesis or recombinant DNA expression. 8. The fusion protein according to any of claims 5-7 wherein said helicase fragment has its carboxy terminus at amino acid 1561 to amino acid 1657. PAGE using a monoclonal antibody against the HCV NS3 protein fragment, the expressed protein was observed only in the soluble part ofthe cell extract. The above materials deposited with the ATCC under the accession numbers indicated, will be maintained under the terms ofthe Budapest Treaty on the International Recognition ofthe Deposit of Microorganisms for purposes of Patent Procedure. These deposits are provided as a convenience to those of skill in the art, and are not an admission that a deposit is required under 35 U.S.C. §112. The polynucleotide sequences contained in the deposited materials, as well as the amino acid sequence ofthe polypeptides encoded thereby, are incoφorated herein by reference and are controlling in the event of any conflict with the sequences described herein. A license may be required to make, use or sell the deposited materials, and no such license is granted hereby.

Claims: -32- contacting said fragment with a compound capable of inhibiting RNA helicase activity; and measuring inhibition ofthe activity of said hepatitis C virus helicase. 17. The method of claim 16 wherein said fragment has its carboxy terminus at amino acid 1561 to amino acid 1657. 18. The method according to either of claims 16 or 17 wherein said fragment has its amino terminus at amino acid 1193 to amino acid 1223. 19. An expression vector for producing HCV NS3 active helicase fragments in a host cell, which vector comprises: a polynucleotide encoding a HCV NS3 helicase fragment having having substantally the same amino acid sequence shown in SEQ ID NO:2; transeriptional and translational regulatory sequences functional in said host cell operably linked to said fragment-encoding polynucleotide; and a selectable marker. 20. The vector of claim 19 further comprising a sequence encoding a fusion partner, linked to said fragment-encoding polynucleotide to form a fusion protein upon expression. 21. The vector of claim 20 wherein said fusion partner is selected from the group consisting of hSOD, yeast alpha- factor, IL-2S, ubiquitin, beta- galactoside, beta-lactamase, horseradish peroxidase, glucose oxidase, and urease. 22. The vector according to any of claims 19-21 , wherein said fragment has its carboxy terminus at amino acid 1561 to amino acid 1657. 9. The fusion protein according to any of claims 5-8 wherein said helicase fragment has its amino terminus at amino acid 1193 to amino acid 1223. 10. The fusion protein according to claim 5 wherein said fusion partner is ubiquitin. 1 1. A composition comprising a polynucleotide which encodes a HCV NS3 helicase fragment having substantailly the amino acid sequence of SEQ ID NO:2. 12. A composition comprising a polynucleotide which encodes a fusion protein comprising a HCV NS3 helicase fragment having substantailly the amino acid sequence of SEQ ID NO:2 and a fusion partner. 13. The composition according to claim 12 wherein said fusion partner is selected from the group consisting of hSOD, yeast alpha-factor, IL-2S, ubiquitin, beta-galactoside, beta-lactamase, horseradish peroxidase, glucose oxidase, and urease. 14. The composition according to either of claims 1 1 or 12, wherein said helicase fragment has its carboxy terminus at amino acid 1561 to amino acid 1657. 15. The composition according to any of claims 1 1-14, wherein said helicase fragment has its amino terminus at amino acid 1193 to amino acid 1223. 16. A method for assaying compounds for activity against hepatitis C virus comprising: providing an HCV NS3 helicase fragment having substantially the same sequence shown in SEQ ID NO:2; 23. The vector according to any of claims 19-22, wherein said fragment has its amino terminus at amino acid 1193 to amino acid 1223.

Inventors: CHOE JOONHO, HANG JANG, CHOE, JOONHO, HANG, JANG
Applicants: CHIRON CORP, CHIRON CORPORATION
Application year: 1996
Main classification: C12N15
IPC codes: A61K38, A61P31, A61P43, C07K14, C07K19, C12N1, C12N9, C12N15, C12R1