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Abstract
The recent approval by the regulatory authorities in the United States of several HIV proteinase inhibitors as therapeutics for the treatment of AIDS confirms that virus proteinases are valid molecular targets in the search for new antiviral drugs. This review summarizes the available approaches that can be taken to discover virus proteinase inhibitors and reviews the current status of our knowledge with respect to virus proteinases in viruses of clinical significance other than HIV. The major focus is on proteinases identified in the viruses that cause the common cold, hepatitis C virus and the herpesviruses.
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Affiliation(s)
- J. S. Mills
- Molecular Virology Department, Roche Research Centre, 40 Broadwater Road, Welwyn Garden City, Herts AL7 3AY, UK
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2
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Pasquetto V, Wieland S, Chisari FV. Intracellular hepatitis B virus nucleocapsids survive cytotoxic T-lymphocyte-induced apoptosis. J Virol 2000; 74:9792-6. [PMID: 11000256 PMCID: PMC112416 DOI: 10.1128/jvi.74.20.9792-9796.2000] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Following antigen recognition, hepatitis B virus (HBV)-specific cytotoxic T lymphocytes (CTL) induce a necroinflammatory liver disease in HBV-transgenic mice. An early event in this process is CTL-dependent activation of apoptosis in a small fraction of HBV-positive hepatocytes. Here we show that cytoplasmic HBV nucleocapsids and their cargo of replicative DNA intermediates survive CTL-induced apoptosis of hepatocytes in vitro. These results suggest that destruction of infected cells per se is not sufficient to destroy the replicating HBV genome in infected tissue and that other events in addition to this process are required for viral clearance to occur.
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Affiliation(s)
- V Pasquetto
- Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California 92037, USA
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3
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Pumpens P, Grens E. Hepatitis B core particles as a universal display model: a structure-function basis for development. FEBS Lett 1999; 442:1-6. [PMID: 9923592 DOI: 10.1016/s0014-5793(98)01599-3] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Because it exhibits a remarkable capability to accept mutational intervention and undergo correct folding and self-assembly in all viable prokaryotic and eukaryotic expression systems, hepatitis B core (HBc) protein has been favored over other proposed particulate carriers. Structurally, the unusual alpha-helical organization of HBc dimeric units allows introduction of foreign peptide sequences into several areas of HBc shells, including their most protruding spikes. Progress toward full resolution of the spatial structure as well as accumulation of chimeric HBc-based structures has brought closer the knowledge-based design of future vaccines, gene therapy tools and other artificial particulate objects.
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Affiliation(s)
- P Pumpens
- Biomedical Research and Study Centre, University of Latvia, Riga.
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4
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Lin CG, Yang SJ, Hwang WL, Su TS, Lo SJ. Demonstration of the presence of protease-cutting site in the spacer of hepatitis B viral Pol protein. J Virol Methods 1995; 51:61-73. [PMID: 7730438 DOI: 10.1016/0166-0934(94)00118-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Molecular genetic studies have revealed that the human hepatitis B viral (HBV) Pol protein, a polypeptide of about 94 kDa, contains four domains. These are the 5'-terminal protein, spacer, RNA reverse transcriptase/DNA polymerase, and RNase H, respectively, from the amino (N) to carboxy (C) terminus. No evidence indicates as yet the involvement of a specific protease in cleaving the Pol protein or the presence of protease-cutting sites in the Pol protein. An in vitro-translated Pol protein was shown to be cleaved by purified thrombin but not in the presence of its inhibitor, hirudin. Two thrombin-cutting sites, spanning 194 amino acids, were then deduced by thrombin digestion of Pol protein with various lengths of C-terminal deletion. These two putative cutting sites, one located in the spacer region and the other in the beginning of the polymerase region, were found to be conserved at similar positions in the Pol protein of all hepadnaviruses. By using a novel method called the LacZ localization assay (LLA), it was demonstrated that a tripartite fusion protein containing the nucleus localization sequence (NLS) of SV40 large T Ag, the putative thrombin cutting sequence (Ile-Arg-Ile-Pro-Arg320-Thr) of HBV Pol protein and the full length beta-galactosidase of E. coli, exhibited a lower percentage (approximately 53%) of targeting into the nucleus of transfected hepatoma cells when compared with a similar tripartite protein containing a single mutation (Arg320 residue into Trp320) of HBV Pol protein (approximately 78%) or with a bipartite protein of SV40 NLS-beta-galactosidase (approximately 90%). These results indicate that the putative thrombin-cutting site in the spacer region of HBV Pol protein could be cleaved by a cellular protease resulting in the separation of NLS sequence from the beta-galactosidase and rendering a lower frequency of X-gal staining in the nucleus.
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Affiliation(s)
- C G Lin
- Graduate Institute of Microbiology and Immunology, National Yang-Ming Medical College, Taipei, Taiwan, R.O.C
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5
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Galle PR, Hagelstein J, Kommerell B, Volkmann M, Schranz P, Zentgraf H. In vitro experimental infection of primary human hepatocytes with hepatitis B virus. Gastroenterology 1994; 106:664-73. [PMID: 8119538 DOI: 10.1016/0016-5085(94)90700-5] [Citation(s) in RCA: 101] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
BACKGROUND/AIMS Studies on the interaction of hepatitis B virus (HBV) with its host cell require a suitable tissue culture system. This study used primary adult hepatocytes from healthy human liver tissue to establish productive infection in vitro. METHODS Hepatocytes were inoculated overnight with HBV. Production of viral proteins was assessed by radioimmunoassay and by [35S]methionine labeling, and production of viral DNA was assessed by Southern blotting and endogenous polymerase assay. RESULTS Secretion of high levels of hepatitis B surface antigen (HBsAg) and low levels of hepatitis B virus e antigen (HBeAg) into the medium was detectable 6 days after infection and reached maximum values after 12 days. Metabolic labeling showed production of viral proteins to be a result of de novo synthesis. The appearance of single-stranded HBV DNA in the cytoplasm of infected cells, typically present in immature cores, indicated viral replication. HBV DNA containing particles possessing an active viral DNA polymerase could be immunoprecipitated from the medium 12 days after infection. An antiserum specific for the preS1 region of the viral envelope was capable to block infection. Presence of dimethyl sulfoxide in the medium greatly improved the yield of viral proteins. CONCLUSIONS Primary adult human liver cells are competent for infection with HBV.
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Affiliation(s)
- P R Galle
- Department of Internal Medicine, University of Heidelberg, Germany
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Rothnie HM, Chapdelaine Y, Hohn T. Pararetroviruses and retroviruses: a comparative review of viral structure and gene expression strategies. Adv Virus Res 1994; 44:1-67. [PMID: 7817872 DOI: 10.1016/s0065-3527(08)60327-9] [Citation(s) in RCA: 101] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- H M Rothnie
- Friedrich Miescher Institute, Basel, Switzerland
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7
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Nassal M. Conserved cysteines of the hepatitis B virus core protein are not required for assembly of replication-competent core particles nor for their envelopment. Virology 1992; 190:499-505. [PMID: 1529550 DOI: 10.1016/0042-6822(92)91242-m] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Replication of hepatitis B virus (HBV) proceeds by reverse transcription of an RNA intermediate inside the viral nucleocapsid formed by the core protein. This protein contains four Cys residues which occur at equivalent positions in the core proteins of all known mammalian hepadnaviruses, suggesting that they might be of structural and/or functional importance. The four His residues of the core protein are located strikingly close to the three N-proximal cysteines. This arrangement is likewise conserved and might indicate the presence of an unconventional Cys-His box element similar to that required for nucleic acid binding in all retroviral NC proteins. In order to test the potential involvement of the core protein cysteines in virus assembly, we transiently expressed in HuH7 cells a mutant HBV genome encoding a core protein in which all cysteines are replaced by serine residues and analyzed the formation of replication-competent cores using the endogenous polymerase reaction. The mutant genome yielded products that were nearly indistinguishable from those produced by a corresponding wild-type genome, virtually ruling out the presence of a functional Cys-His box element in the hepadnaviral core protein. Density gradient analysis showed that the mutant cores were enveloped, though the efficiency of envelopment and/or the stability of the mutant enveloped particles was lowered compared to the wild-type. These data indicate that none of the steps in the viral life cycle from reverse transcription to envelopment was principally impaired. The conservedness of the cysteines might then be related to virus infectivity rather than replication; alternatively, the Cys residues might not be important for the core protein itself, but for the alternative C gene product HBeAg.
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Affiliation(s)
- M Nassal
- Zentrum für Molekulare Biologie, Universität Heidelberg, Germany
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8
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Nassal M. The arginine-rich domain of the hepatitis B virus core protein is required for pregenome encapsidation and productive viral positive-strand DNA synthesis but not for virus assembly. J Virol 1992; 66:4107-16. [PMID: 1602535 PMCID: PMC241213 DOI: 10.1128/jvi.66.7.4107-4116.1992] [Citation(s) in RCA: 360] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Assembly of replication-competent hepatitis B virus (HBV) nucleocapsids requires the interaction of the core protein, the P protein, and the RNA pregenome. The core protein contains an arginine-rich C-terminal domain which is dispensable for particle formation in heterologous expression systems. Using transient expression in HuH7 cells of a series of C-terminally truncated core proteins, I examined the functional role of this basic region in the context of a complete HBV genome. All variants containing at least the 144 N-terminal amino acids were assembly competent, but efficient pregenome encapsidation was observed only with variants consisting of 164 or more amino acids. These data indicate that one function of the arginine-rich region is to provide the interactions between core protein and RNA pregenome. However, in cores from the variant ending with amino acid 164, the production of complete positive-strand DNA was drastically reduced. Moreover, almost all positive-strand DNA originated from in situ priming, whereas in wild-type particles, this type of priming not supporting the formation of relaxed circular DNA (RC-DNA) accounted for about one half of the positive strands. Further C-terminal residues to position 173 restored RC-DNA formation, and the corresponding variant did not differ from the full-length core protein in all assays used. The observation that RNA encapsidation and formation of RC-DNA can be genetically separated suggests that the core protein, via its basic C-terminal region, also acts as an essential auxiliary component in HBV replication, possibly like a histone, or like a single-stranded-DNA-binding protein. In contrast to their importance for HBV replication, sequences beyond amino acid 164 were not required for the formation of enveloped virions. Since particles from variant 164 did not contain mature DNA genomes, a genome maturation signal is apparently not required for HBV nucleocapsid envelopment.
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Affiliation(s)
- M Nassal
- Zentrum für Molekulare Biologie, Universität Heidelberg, Germany
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9
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Chen Y, Robinson WS, Marion PL. Naturally occurring point mutation in the C terminus of the polymerase gene prevents duck hepatitis B virus RNA packaging. J Virol 1992; 66:1282-7. [PMID: 1309904 PMCID: PMC240843 DOI: 10.1128/jvi.66.2.1282-1287.1992] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
A duck hepatitis B virus (DHBV) genome cloned from a domestic duck from the People's Republic of China has been sequenced and exhibits no variation in sequences known to be important in viral replication or generation of gene products. Intrahepatic transfection of a dimer of this viral genome into ducklings did not result in viremia or any sign of virus infection, indicating that the genome was defective. Functional analysis of this mutant genome, performed by transfecting the DNA into a chicken hepatoma cell line capable of replicating wild-type virus, indicated that viral RNA is not encapsidated. However, virus core protein is made and can assemble into particles in the absence of encapsidation of viral nucleic acid. Using genetic approaches, it was determined that a change of cysteine to tyrosine in position 711 in the polymerase (P) gene C terminus led to this RNA-packaging defect. By site-directed mutagenesis, it was found that while substitution of Cys-711 with tryptophan also abolished packaging, substitution with methionine did not affect packaging or viral replication. Therefore, Cys-711, which is conserved in all published sequences of DHBV, may not be involved in a disulfide bridge structure essential to viral RNA packaging or replication. Our results, showing that a missense mutation in the region of the DHBV polymerase protein thought to be primarily the RNase H domain results in packaging deficiency, support the previous findings that multiple regions of the complex hepadnaviral polymerase protein may be required for viral RNA packaging.
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MESH Headings
- Amino Acid Sequence
- Animals
- Blotting, Southern
- Capsid/analysis
- Capsid/physiology
- Cell Line
- Chickens
- Cloning, Molecular
- DNA, Viral/genetics
- DNA-Directed RNA Polymerases/genetics
- Ducks
- Genes, Viral
- Genome, Viral
- Hepatitis B Virus, Duck/enzymology
- Hepatitis B Virus, Duck/genetics
- Mutagenesis, Site-Directed
- Mutation
- RNA, Viral/genetics
- RNA, Viral/metabolism
- Ribonuclease H/genetics
- Transfection
- Viral Core Proteins/analysis
- Viral Core Proteins/physiology
- Virus Replication
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Affiliation(s)
- Y Chen
- Department of Medicine, Stanford University School of Medicine, California 94305-5107
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10
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Schlicht HJ, Wasenauer G. The quaternary structure, antigenicity, and aggregational behavior of the secretory core protein of human hepatitis B virus are determined by its signal sequence. J Virol 1991; 65:6817-25. [PMID: 1942254 PMCID: PMC250773 DOI: 10.1128/jvi.65.12.6817-6825.1991] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Human hepatitis B virus encodes a secretory core protein, referred to as the HBe protein, whose secretion is mediated by the pre-C signal sequence. Here we examined whether this sequence is important only for translocation of the HBe precursor (the precore protein) or whether it also contributes to the structural and biophysical properties of the mature HBe protein. When a truncated hepatitis B virus precore protein, lacking the basic C-terminal domain which is cleaved from the wild-type protein during its conversion into HBe, was expressed in human hepatoma cells, only a small amount of HBe-like protein was produced. This protein was slightly smaller than the wild-type HBe protein, suggesting that C-terminal cleavage of the precore protein does not occur at the suggested site. When the authentic signal sequence of the precore protein (the pre-C sequence) was replaced by the unrelated signal sequence of an influenza virus hemagglutinin, not only the full-length but also the C-terminally truncated protein was expressed and secreted with high efficiency. Western blot (immunoblot) analyses with nonreducing gels and conformation-specific monoclonal antibodies revealed that the HBe protein secreted under control of the pre-C signal sequence was a monomer with HBe antigenicity, whereas the HBe-like protein secreted under control of the hemagglutinin signal sequence was a disulfide-bridge-linked dimer with both HBe and HBc antigenicity. Electron microscopic examination of gradient-purified particulate core gene products showed that HBe protein secreted under control of the hemagglutinin signal sequence forms core particles, whereas HBe protein secreted under control of the pre-C sequence does not. Thus, the pre-C sequence not only mediates the secretion but also determines the structural and aggregational properties of the HBe protein.
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Affiliation(s)
- H J Schlicht
- Department of Virology, University of Ulm, Germany
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11
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Abstract
Reverse transcription is not solely a retroviral mechanism. Hepadnaviruses and caulimoviruses have RNA intermediates that are reverse transcribed into DNA. Moreover non-viral retroelements, retrotransposons, use reverse transcription in their transposition. All these retroelements encode reverse transcriptase but each group developed their own expression modes capable of assuring a specific and efficient replication of their genomes.
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Affiliation(s)
- J M Mesnard
- Institut de Biologie Moléculaire des Plantes du C.N.R.S., Université Louis Pasteur, Strasbourg, France
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12
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Schlicht HJ. Biosynthesis of the secretory core protein of duck hepatitis B virus: intracellular transport, proteolytic processing, and membrane expression of the precore protein. J Virol 1991; 65:3489-95. [PMID: 2041077 PMCID: PMC241336 DOI: 10.1128/jvi.65.7.3489-3495.1991] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The biosynthesis of the secretory core gene product of the duck hepatitis B virus (DHBe protein) was examined. Recombinant vaccinia viruses were constructed encoding either the full-length or C-terminally truncated forms of the DHBe precursor protein (precore protein) and used to express these proteins in the human hepatoma cell line HepG2. Western immunoblot analysis of core gene products isolated from cells producing the full-length precore protein revealed the presence of DHBe precursor proteins containing the strongly basic C-terminal sequence which is lacking in the mature DHBe protein. These proteins were not secreted, suggesting that C-terminal proteolytic processing of the precore protein represents an obligatory step for DHBe biosynthesis. Pulse-chase experiments showed that this cleavage reaction occurs late during DHBe synthesis. Interestingly, when mutated precore proteins were expressed which lacked the basic C-terminal domain, proteins were produced which were glycosylated but not secreted. This shows that the transient presence of this region is essential for intracellular transport of the precore protein. Cell sorter analyses revealed that production of a cell surface-expressed variant of the secretory core protein is a feature conserved between the duck and the human hepatitis B viruses. Surprisingly, the C terminus of the membrane-expressed DHBe protein was accessible from the outside, showing that the topology of this interesting protein is more complicated than expected.
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Affiliation(s)
- H J Schlicht
- Department of Virology, University of Ulm, Germany
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13
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Affiliation(s)
- D Ganem
- Department of Microbiology and Immunology, University of California Medical Center, San Francisco 94143-0503
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14
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Marion PL. Development of antiviral therapy for chronic infection with hepatitis B virus. Curr Top Microbiol Immunol 1991; 168:167-83. [PMID: 1893776 DOI: 10.1007/978-3-642-76015-0_8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- P L Marion
- Department of Medicine, Stanford University School of Medicine, CA 94305
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15
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Jean-Jean O, Salhi S, Carlier D, Elie C, De Recondo AM, Rossignol JM. Biosynthesis of hepatitis B virus e antigen: directed mutagenesis of the putative aspartyl protease site. J Virol 1989; 63:5497-500. [PMID: 2685358 PMCID: PMC251224 DOI: 10.1128/jvi.63.12.5497-5500.1989] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The C gene products of all mammalian hepadnaviruses contain a region with sequence similarities to the catalytic center of the aspartyl proteases. This region could have the capacity to cleave precore proteins, leading to the synthesis of e antigen. By site-directed mutagenesis on a plasmid containing the hepatitis B virus C gene, we have replaced either the Asp residue of the putative aspartyl protease catalytic center or an Asp residue located 3 amino acids upstream. Transient expression of the mutated hepatitis B virus C gene in human and mouse cells showed that none of these mutations prevented the secretion of an accurately processed HBe antigen. Thus, we demonstrated that the aspartyl protease responsible for e antigen precursor processing is not C gene encoded but is more likely to be a cellular enzyme. From these results, we suggest a model for the mechanism of e antigen synthesis.
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Affiliation(s)
- O Jean-Jean
- Laboratoire de Biologie Moléculaire de la Réplication, ER 272-Centre National de la Recherche Scientifique, Villejuif, France
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