DNA of a Human Hepatitis B Virus Candidate

Particles containing DNA polymerase (Dane particles) were purified from the plasma of chronic carriers of hepatitis B antigen. After a DNA polymerase reaction with purified Dane particle preparations treated with Nonidet P-40 detergent, Dane particle core structures containing radioactive DNA product were isolated by sedimentation in a sucrose density gradient. The radioactive DNA was extracted with sodium dodecyl sulfate and isolated by band sedimentation in a preformed CsCl gradient. Examination of the radioactive DNA band by electron microscopy revealed exclusively circular double-stranded DNA molecules approximately 0.78 mum in length. Identical circular molecules were observed when DNA was isolated by a similar procedure from particles that had not undergone a DNA polymerase reaction. The molecules were completely degraded by DNase 1. When Dane particle core structures were treated with DNase 1 before DNA extraction, only 0.78-mum circular DNA molecules were detected. Without DNase treatment of core structures, linear molecules with lengths between 0.5 and 12 mum, in addition to the 0.78-mum circles were found. These results suggest that the 0.78-mum circular molecules were in a protected position within Dane particle cores and the linear molecules were not within core structures. Length measurements on 225 circular molecules revealed a mean length of 0.78 +/- 0.09 mum which would correspond to a molecular weight of around 1.6 x 10(6). The circular molecules probably serve as primer-template for the DNA polymerase reaction carried out by Dane particle cores. Thermal denaturation and buoyant density measurements on the Dane particle DNA polymerase reaction product revealed a guanosine plus cytosine content of 48 to 49%.     

Evidence for supercoiled hepatitis B virus DNA in chimpanzee liver and serum Dane particles: possible implications in persistent HBV infection

In chimpanzee hepatitis B virus (HBV) carriers, the mechanism of viral persistence has been examined by analyzing viral DNA molecules in liver and serum. Chimpanzee liver DNA contained two extrachromosomal HBV DNA molecules migrating on hybridization blots at 4.0 kb and 2.3 kb. There was no evidence for integration of HBV DNA into the host genome. The extrachromosomal molecules were distinct from Dane particle DNA and were converted to linear 3.25 kb full-length double-stranded HBV DNA on digestion with Eco RI. Nucleases S1 and Bal 31 converted "2.3 kb" HBV DNA to 3.25 kb via an intermediate of "4.0 kb" apparent length. The HBV DNA molecule that migrated at 2.3 kb represents a supercoiled form I of the HBV genome, and the molecule that migrated at 4.0 kb represents a full-length "nicked," relaxed circular form II. Evidence for supercoiled HBV DNA in serum Dane particles was obtained by production of form II molecules upon digestion with nuclease S1 or Bal 31. It is proposed that most Dane particles represent interfering noninfectious virus containing partially double-stranded DNA circles and that particles containing supercoiled HBV DNA may represent infectious hepatitis B virus.     

Model for the supercoiling reaction catalyzed by DNA gyrase

A hypothesis is presented which suggests that hepatitis B DNA in the Dane particles is only a partial viral genome which becomes integrated into the hepatocyte cellular DNA. The Dane particle DNA must enter a liver cell containing an active e gene, in order to become functional. It is suggested that the partial genome of hepatitis B virus is released from the cellular DNA by the mechanism of “escaping genes”.     

Structure of Hepatitis B Dane Particle DNA and Nature of the Endogenous DNA Polymerase Reaction

The circular DNA of hepatitis B Dane particles, which serves as the primer/template for an endogenous DNA polymerase, was analyzed by electrophoresis before and after a polymerase reaction and after digestion by restriction endonuclease or single-strand-specific endonuclease S1. The unreacted molecules extracted from the particles were electrophoretically heterogeneous, and treatment with S1 nuclease produced double-stranded linear DNA ranging in length from 1,700 to 2,800 base pairs (bp). After an endogenous DNA polymerase reaction, two discrete species of DNA molecules were found: a circular form and a linear form 3,200 bp long. The reaction resulted in a population of molecules with an elongated and more homogeneous double-stranded region. These results suggest that the circular molecules in Dane particles have single-stranded regions of varying lengths that are made double stranded during the DNA polymerase reaction. The endogenous DNA polymerase was found to initiate apparently at random in a region spanning more than a third of the molecule. Analysis of restriction endonuclease cleavage fragments of the fully elongated DNA revealed that although the molecules were of a uniform length, they were somewhat heterogeneous in sequence. The sum of the sizes of the 10 major endonuclease Hae III-generated fragments, detected by ethidium bromide, was 3,880 bp. Two additional fragments (B and G) detected by autoradiography after an endogenous DNA polymerase reaction with (32)P-labeled deoxynucleoside triphosphates made the total 4,910 bp.     

Three envelope proteins of hepatitis B virus: large S, middle S, and major S proteins needed for the formation of Dane particles.

The infectious particles of hepatitis B virus are called Dane particles and consist of viral nucleic acid encapsulated within a core particle that is enveloped by virus-coded surface proteins. The major S protein constitutes a significant fraction of these surface proteins. In addition, there are two other related proteins (large S and middle S), but their role in envelope formation has not yet been elucidated. We modified the translation initiation codon ATG of each of the envelope proteins by site-directed mutagenesis and found that mutant genomes that did not produce one or two of these proteins were unable to form Dane particles. The particles released into the culture medium by such mutants did not carry DNA. Synthesis of virus-coded RNA still occurred normally, and core particles carrying DNA accumulated intracellularly. The DNA in such core particles was mostly in the double-stranded open circular form, in contrast to the normal situation in which the particles contain mostly RNA and its complementary single-stranded DNA or else contain linear DNA that is partially single stranded and otherwise duplex. The role of the large S and middle S proteins in the formation of Dane particles is discussed.     

Protein Kinase Activity in Hepatitis B Virus

Protein kinase activity was found in hepatitis B virions (Dane particles) purified from the plasma of hepatitis B virus-infected patients, in virion cores, and in hepatitis B core antigen particles purified from hepatitis B virus-infected hepatic tissue and was not found in purified hepatitis B surface antigen particle preparations free of Dane particles. Only a fraction of the major polypeptide (apparent size, 19,700 daltons) in Dane particle cores and hepatitis B core antigen particles from infected liver appeared to be phosphorylated, and phosphorylation changed the electrophoretic mobility in sodium dodecyl sulfate-polyacrylamide gels to that expected for a polypeptide of 20,600 daltons. Five minor polypeptides with apparent sizes between 38,000 and 63,000 daltons were phosphorylated in Dane particles and Dane particle core preparations but were not detected in hepatitis B core antigen particles from infected liver. None of these had electrophoretic mobilities corresponding to those of known hepatitis B surface antigen polypeptides. Prolonged storage of purified hepatitis B core antigen particles or incubation with human immunoglobulin G preparations containing antibody to the hepatitis B core antigen with or without antibody to the hepatitis B e antigen resulted in the conversion of the polypeptide with an apparent size of 20,600 daltons to ones with apparent sizes of 14,700 and approximately 6,000 daltons, suggesting proteolytic cleavage of the 20,600-dalton polypeptide under these conditions.     

血源乙肝疫苗的电镜制样方法

用作样品支持物喷碳的铜网,磷钨酸染色制备血源乙肝疫苗电镜检测样品。４９３批血源乙肝疫苗的镜检结果显示：经溴化钾和蔗糖离心后,原料血浆中的Ｄａｎｅ颗粒和管形颗粒已去除,只观察到２２－２４纳米的ＨＢｓＡｇ球形颗粒。     

DNA Polymerase in the Core of the Human Hepatitis B Virus Candidate

Experiments were done to show that the human hepatitis B antigen (HBAg)-associated DNA polymerase is a component of Dane particles and their antigenically distinct cores prepared by Nonidet P-40 detergent treatment of Dane particles. Before detergent treatment, the DNA polymerase was precipitated by serum containing anti-HB surface antigen (anti-HB(s)) but not with serum containing anti-HB core antigen (anti-HB(c)). After detergent treatment, the enzyme was precipitated by anti-HB(c)- and not by anti-HB(s)-containing serum. Highly purified 16- to 25-nm HBAg particles blocked only the precipitation of DNA polymerase in untreated HBAg preparations. The 110S structure with which the DNA reaction product remains associated in Nonidet P-40-treated preparations was identified as Dane particle core by immunoprecipitation with serum containing anti-HB(c). The DNA polymerase and the radioactive DNA reaction product were used as markers for core in immunoprecipitation tests for anticore. In such assays, 8 of 11 human sera with anti-HB(s) activity and all of 10 sera from chronic HBAg carriers were found to contain anti-HB(c) activity.     

Structure of hepatitis B Dane particle DNA before and after the Dane particle DNA polymerase reaction.

DNA isolated from the hepatitis B antigen form known as the Dane particle was examined by electron microscopy before and after the endogenous Dane particle DNA polymerase reaction. The most frequently occurring form was an untwisted circular double-stranded DNA molecule approximately 1 mum in length. Less frequently occurring forms included circular DNA of approximately unit length and having one or more small single-stranded regions, similar circular molecules with one or more tails either shorter or longer than 1 mum in length, and very small circular molecules with tails. There was no increase in frequency or length of tails after a DNA polymerase reaction, suggesting that tails were not formed during this reaction. The mean length of circular molecules increased by 23% when DNA was spread in formamide compared with aqueous spreading, suggesting that single-stranded regions are present in most of the molecules. The mean length of circular molecules obtained from aqueous spreading increased by 27% after a Dane particle DNA polymerase reaction. This indicates that single-stranded regions were converted to double-stranded DNA during the reaction.     

HBsAg-positive chronic liver disease: inhibition of DNA polymerase activity by vidarabine.

Four patients who had chronic liver disease and were positive for hepatitis B surface antigen (HBsAg) were treated with vidarabine, a synthetic purine nucleoside that inhibits DNA polymerase activity in vitro and in vivo. Before treatment all had raised serum DNA polymerase concentrations. Three also had hepatitis B e (HBe) and were shown by electron microscopy to have hepatitis B virus (Dane) particles in their serum. In all patients 10 days'' treatment with vidarabine resulted in an immediate loss of DNA polymerase activity. In three patients the activity returned when treatment was stopped. In those three patients Dane particles and HBe antigen persisted during and after treatment; in the fourth patient, who remained negative for DNA polymerase, HBsAg titres fell. Although vidarabine inhibited virus replication, virus particles did not disappear from the blood in these patients, presumably because the particles were cleared only slowly. Similar results with interferon suggest that the virus disappears, and HBsAg titres fall, some weeks after the fall in DNA polymerase activity. Continued treatment may therefore have a sustained effect on viral replication. Whether vidarabine can permanently clear HBsAg and so arrest chronic liver disease remains to be seen, but at the very least it could reduce the spread of infection.     

Inhibition of hepatitis B Dane particle DNA polymerase activity by pyrophosphate analogs

A DNA polymerase is associated with the core of the so-called Dane particles. The probability that this is the hepatitis B viral DNA polymerase offers the possibility of preventing hepatitis B multiplication by selective inhibition of this enzyme. We have previously reported that trisodium phosphonoformate (PFA) inhibits Dane particle DNA polymerase. Fifteen compounds with structural similarity to PFA and pyrophosphate have now been tested for inhibition of hepatitis B virus DNA polymerase in an attempt to define the structural requirement for the inhibition. Active structures have two acid groups at close proximity of which at least one is a phosphono group. Phosphonoformate and hypophosphare were the two most active inhibitors. The Ki value for PFA was 7.2 microM when dTTP was used as variable substrate, and the mechanism of inhibition was non-competitive. Phosphonoformate caused rapid shut-off of the polymerase reaction, indicating that it might inhibit elongation. The efficient inhibition of hepatitis B virus DNA polymerase by PFA and its low toxicity suggest that it could be used to inhibit hepatitis B virus multiplication in vivo.     

Characterization of viral genomes in the liver and serum of chimpanzee long-term hepatitis B virus carriers: a possible role for supercoiled HBV-DNA in persistent HBV infection

In chimpanzee hepatitis B virus (HBV) carriers, the molecular mechanism for viral persistence has been examined by analyzing the properties of viral DNA molecules in liver and serum. Two extrachromosomal HBV-DNA molecules migrating on Southern blots at 4.0 kb and 2.3 kb were observed in chimpanzee liver DNA. There was no evidence for integration of HBV sequences into the host genome. The HBV-DNA molecule which migrated at 4.0 kb position represents a full-length "nicked," relaxed circular form, and the DNA molecules migrating at 2.3 kb position represents a supercoiled form of the HBV genome. Evidence for supercoiled HBV-DNA in serum was obtained by production of the relaxed circular intermediate upon digestion of Dane particle DNA with specific nucleases S1 and Bal 31. A possible role of these two extrachromosomal HBV-DNA molecules in the biology of hepatitis B virus infection and the mechanism for viral persistence are discussed.     

Production of hepatitis B virus in vitro by transient expression of cloned HBV DNA in a hepatoma cell line.

Transfection of human hepatoma cell lines with cloned HBV DNA resulted in the secretion of large amounts of hepatitis B surface antigen (HBsAg) and core-related antigens (HBc/HBeAg) if well-differentiated cell lines were employed. Synthesis of both viral antigens was the highest in cell line HuH-7 and continued for approximately 25 days. Particles resembling hepatitis B virions (Dane particles) by morphology, density and by the presence of the preS1 surface antigen were released from the transfected HuH-7 cells into the culture medium. These particles produced in vitro were also indistinguishable from the naturally occurring hepatitis B virions in containing the virus-associated DNA polymerase and mature HBV genomes. Restriction analysis of these DNA molecules was compatible with the nucleotide sequence of the transfecting HBV DNA sequence. Viral surface antigens and core proteins present in the culture medium were fractionated and characterized by immunoprecipitation and SDS--PAGE after labeling with [35S]methionine. Antisera specific for X-gene products identified in cell extracts two hitherto unknown HBV gene products. This system thus provides a new approach to open questions regarding HBV-related gene function and HBV replication.     

DNA contained by two densonucleosis viruses.

The DNA contained by particles of densonucleosis viruses 1 and 2 were analyzed within the particle, and properties of DNA extracted from these particles were determined. The DNA appears to exist as a single-stranded molecule with limited secondary structure within particles, as assessed by spectral changes induced by formaldehyde, melting profiles, and circular dichroism studies. The single-stranded DNA had an apparent molecular weight of 1.9 X 10(6) to 2.2 X 10(6) as assessed by differences in the molecular weight of virus particles and top component and percentage of nucleic acid. DNA extracted from virus particles in low-salt buffers possessed properties typical of a single-stranded molecule. Double-stranded DNA could be extracted from virus particles under appropriate high salt and elevated temperature. The linear double-stranded DNA extracted from both viruses had a molecular weight of about 3.9 X 10(6) to 4.1 ZX 10(6) determined by neutral sedimentation and electron microscopy and an equivalent genome size determined by reassociation kinetics. About 87% of the DNA was homologous between the two viruses.     

Hepatitis B Core Antigen: Immunology and Electron Microscopy

TWO DISTINCT VIRAL ANTIGENS ARE ASSOCIATED WITH THE HEPATITIS B VIRUS: the hepatitis B surface antigen (HB(s)Ag, Australia antigen) and the hepatitis B core antigen (HB(c)Ag). HB(s)Ag, purified from the serum of asymptomatic human HB(s)Ag carriers, and HB(c)Ag, purified from the liver of a chimpanzee acutely infected with hepatitis B virus, were examined by serological and immune electron microscopic methods. Antisera raised against HB(s)Ag reacted with the outer, surface component of the Dane particle and with the 20-nm spherical and tubular particles present in HB(s)Ag-positive serum, but not with the internal component of the Dane particle or with purified HB(c)Ag particles. Antisera raised against purified HB(c)Ag particles reacted with the internal component of the Dane particle and with HB(c)Ag, but not with the surface of the Dane particle or with the 20-nm spherical and tubular particles associated with HB(s)Ag. Purified HB(c)Ag particles, 27 nm in diameter, demonstrated distinct subunits. The infectious form of hepatitis B virus appears to be represented by the 42-nm Dane particle composed of a 27-nm nucleocapsid core component (HB(c)Ag) surrounded by an antigenically and morphologically distinct lipoprotein surface component (HB(s)Ag).     

Hepatitis B virus DNA-negative dane particles lack core protein but contain a 22-kDa precore protein without C-terminal arginine-rich domain

DNA-negative Dane particles have been observed in hepatitis B virus (HBV)-infected sera. The capsids of the empty particles are thought to be composed of core protein but have not been studied in detail. In the present study, the protein composition of the particles was examined using new enzyme immunoassays for the HBV core antigen (HBcAg) and for the HBV precore/core proteins (core-related antigens, HBcrAg). HBcrAg were abundant in fractions slightly less dense than HBcAg and HBV DNA. Three times more Dane-like particles were observed in the HBcrAg-rich fraction than in the HBV DNA-rich fraction by electron microscopy. Western blots and mass spectrometry identified the HBcrAg as a 22-kDa precore protein (p22cr) containing the uncleaved signal peptide and lacking the arginine-rich domain that is involved in binding the RNA pregenome or the DNA genome. In sera from 30 HBV-infected patients, HBcAg represented only a median 10.5% of the precore/core proteins in enveloped particles. These data suggest that most of the Dane particles lack viral DNA and core capsid but contain p22cr. This study provides a model for the formation of the DNA-negative Dane particles. The precore proteins, which lack the arginine-rich nucleotide-binding domain, form viral RNA/DNA-negative capsid-like particles and are enveloped and released as empty particles.     

Titration of integrated simian virus 40 DNA sequences, using highly radioactive, single-stranded DNA probes.

Nick-translated simian virus 40 (SV40) [32P]DNA fragments (greater than 2 X 10(8) cpm/micrograms) were resolved into early- and late-strand nucleic acid sequences by hybridization with asymmetric SV40 complementary RNA. Both single-stranded DNA fractions contained less than 0.5% self-complementary sequences; both included [32P]-DNA sequences that derived from all regions of the SV40 genome. In contrast to asymmetric SV40 complementary RNA, both single-stranded [32P]DNAs annealed to viral [3H]DNA at a rate characteristic of SV40 DNA reassociation. Kinetics of reassociation between the single-stranded [32P]DNAs indicated that the two fractions contain greater than 90% of the total nucleotide sequences comprising the SV40 genome. These preparations were used as hybridization probes to detect small amounts of viral DNA integrated into the chromosomes of Chinese hamster cells transformed by SV40. Under the conditions used for hybridization titrations in solution (i.e., 10- to 50-fold excess of radioactive probe), as little as 1 pg of integrated SV40 DNA sequence was assayed quantitatively. Among the transformed cells analyzed, three clones contained approximately one viral genome equivalent of SV40 DNA per diploid cell DNA complement; three other clones contained between 1.2 and 1.6 viral genome equivalents of SV40 DNA; and one clone contained somewhat more than two viral genome equivalents of SV40 DNA. Preliminary restriction endonuclease maps of the integrated SV40 DNAs indicated that four clones contained viral DNA sequences located at a single, clone-specific chromosomal site. In three clones, the SV40 DNA sequences were located at two distinct chromosomal sites.     

Amplification and rearrangement in hepatoma cell DNA associated with integrated hepatitis B virus DNA.

DNA of hepatitis B virus is found to be integrated into the genome of infected human liver cells and may be related to the development of primary liver carcinoma. We have previously reported the cloning of cellular DNA with integrated HBV sequences from the PLC/PRF/5 cell line which derives from a human primary liver carcinoma. Two clones, designated as A-10.7 and A-10.5, and a third uncloned fragment are compared by restriction enzyme mapping, hybridization and nucleotide sequencing. The results indicate that amplification of integrated viral DNA and host flanking regions has occurred, followed by transposition and/or major deletions. The implications of these findings for the development of primary liver carcinoma are discussed.