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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The hepatitis B virus (HBV), the causal agent of serum hepatitis, has a diameter of 42 nm and is comprised of an outer surface coat and a 27 nm core. A unique DNA-dependent DNA polymerase is associated with the core of the virus. The core also houses a circular DNA that contains both double-stranded and single-stranded regions. In the endogenous reaction, the DNA polymerase repairs the single-stranded gaps of the viral DNA. The surface protein of the virus, called hepatitis B surface antigen, contains both lipid and carbohydrate, and is often present in particulate form in the blood of infected patients. In Asia and Africa HBV infection is associated with subsequent development of primary hepatocellular carcinoma. Although most patients recover completely from acute illness, the hepatitis B virus may cause chronic infection. Recently, a virus similar to human HBV was discovered in woodchucks. HBV has not yet been propagated in a cell culture system and the mode of replication of this unusual virus in hepatocytes is still moot. Although reliable therapy has not yet been provided, the problem of this world-wide infection has led to many interesting approaches to both vaccine production and anti-viral chemotherapy.
Mol Cell Biochem 1979 Jul 15
PMID:The hepatitis B virus and its DNA polymerase: the prototype three-D virus. 9 Oct 92

Reverse transcriptase (RT) was first discovered as an essential catalyst in the biological cycle of retroviruses. However, in the past years evidence has accumulated showing that RTs are involved in a surprisingly large number of RNA-mediated transpositional events that include both viral and nonviral genetic entities. Although it is probable that some RT-bearing genetic elements like the different types of AIDS viruses and the mammalian LINE family have arisen in recent geological times, the possibility that reverse transcription first took place in the early Archean is supported by (1) the hypothesis that RNA preceded DNA as cellular genetic material; (2) the existence of homologous regions of the subunit tau of the E. coli DNA polymerase III with the simian immunodeficiency virus RT, the hepatitis B virus RT, and the beta' subunit of the E. coli RNA polymerase (McHenry et al. 1988); (3) the presence of several conserved motifs, including a 14-amino-acid segment that consists of an Asp-Asp pair flanked by hydrophobic amino acids, which are found in all RTs and in most cellular and viral RNA polymerases. However, whether extant RTs descend from the primitive polymerase involved in the RNA-to-DNA transition remains unproven. Substrate specificity of the AMV and HIV-1 RTs can be modified in the presence of Mn2+, a cation which allows them to add ribonucleotides to an oligo (dG) primer in a template-dependent reaction. This change in specificity is comparable to that observed under similar conditions in other nucleic acid polymerases. This experimentally induced change in RT substrate specificity may explain previous observations on the misincorporation of ribonucleotides by the Maloney murine sarcoma virus RT in the minus and plus DNA of this retrovirus (Chen and Temin 1980). Our results also suggest that HIV-infected macrophages and T-cell cells may contain mixed polynucleotides containing both ribo- and deoxyribonucleotides. The evolutionary significance of these changes in substrate specificities of nucleic acid polymerases is also discussed.
J Mol Evol 1992 Dec
PMID:On the early emergence of reverse transcription: theoretical basis and experimental evidence. 128 61

The polyadenylation signal for the late mRNAs of simian virus 40 is known to have sequence elements located both upstream and downstream of the AAUAAA which affect efficiency of utilization of the signal. The upstream efficiency element has been previously characterized by using deletion mutations and transfection analyses. Those studies suggested that the upstream element lies between 13 and 48 nucleotides upstream of the AAUAAA. We have utilized in vitro cleavage and polyadenylation reactions to further define the upstream element. 32P-labeled substrate RNAs were prepared by in vitro transcription from wild-type templates as well as from mutant templates having deletions and linker substitutions in the upstream region. Analysis of these substrates defined the upstream region as sequences between 13 and 51 nucleotides upstream of the AAUAAA, in good agreement with the in vivo results. Within this region, three core elements with the consensus sequence AUUUGURA were identified and were specifically mutated by linker substitution. These core elements were found to contain the active components of the upstream efficiency element. Using substrates with both single and double linker substitution mutations of core elements, we observed that the core elements function in a distance-dependent manner. In mutants containing only one core element, the effect on efficiency increases as the distance between the element and the AAUAAA decreases. In addition, when core elements are present in multiple copies, the effect is additive. The core element consensus sequence, which bears homology to the Sm protein complex-binding site in human U1 RNA, is also found within the upstream elements of the ground squirrel hepatitis B and cauliflower mosaic virus polyadenylation signals (R. Russnak, Nucleic Acids Res. 19:6449-6456, 1991; H. Sanfacon, P. Brodmann, and T. Hohn, Genes Dev. 5:141-149, 1991), suggesting functional conservation of this element between mammals and plants.
Mol Cell Biol 1992 Dec
PMID:Definition of the upstream efficiency element of the simian virus 40 late polyadenylation signal by using in vitro analyses. 133 42

As the polymerase chain reaction (PCR) can be used for the generation of vector-free probes, the optimum conditions for incorporation of digoxigenin-11-dUTP into hepatitis B virus (HBV) probes have been investigated. High yields of double-stranded or single-stranded probes can be obtained by utilizing a pair of primers or one primer alone. The probes were tested by dot-blot hybridization on HBV plasmid DNA, slot-blot hybridization on total cellular RNA of Alexander cells and Southern blot hybridization on cellular DNA of Alexander cells and HBV plasmid DNA. They were also tested by in situ hybridization (ISH) on HBV-positive biopsy liver tissue. A ratio of dig-dUTP:dTTP of 1:3 gave highest sensitivity in DNA hybridization. No loss of amplification efficiency and sensitivity was observed when the final concentration of dig-11-dUTP and dTTP was reduced to 20 microM and 60 microM respectively, compared to 200 microM each of dATP, dCTP, dGTP. Several different sizes of double-strand probes were compared by dot-blot hybridization. Longer probes were more sensitive. Strong signal could also be obtained by combination of two or three small probes, which have overlapping sequences. Single-stranded DNA probes had advantages of simplicity of use, high sensitivity and strand specificity.
Mol Cell Probes 1992 Jun
PMID:Generation of digoxigenin-labelled double-stranded and single-stranded probes using the polymerase chain reaction. 140 27

The nucleocapsid, or core particle, of hepatitis B virus is formed by 180 subunits of the core protein, which contains Cys at positions 48, 61, 107 and 183, the latter constituting the C terminus. Upon adventitious oxidation, some or all of these cysteine residues participate in the formation of disulphide bridges, leading to polymerization of the subunits within the particle. To utilize the cysteine residues as topological probes, we reduced the number of possible intersubunit crosslinks by replacing these residues individually, or in all combinations, by serine. A corresponding set of variants was constructed within the context of an assembly-competent core protein variant that lacks the highly basic C-terminal region. Analysis, by polyacrylamide gel electrophoresis under non-reducing conditions, of the oxidative crosslinking products formed by the wild-type and mutant proteins expressed in Escherichia coli, revealed a clear distinction between the three N-proximal, and the C-terminal Cys: N-proximal Cys formed intermolecular disulphide bonds only with other N-proximal cysteine residues, leading to dimerization. Cys48 and Cys61, in contrast to Cys107, could be crosslinked to the homologous cysteine residues in a second subunit, and are therefore located at the dimer interface. Cys 183 predominantly formed disulphide bonds with Cys183 in subunits other than those crosslinked by the N-proximal cysteine residues. Hence, the polymers generated by oxidation of the wild-type protein are S-S-linked dimeric N-terminal domains interconnected via Cys183/Cys183 disulphide bonds. The intermolecular crosslinks between the N-proximal cysteine residues were apparently the same in the C-terminally truncated and in the full-length proteins, corroborating the model in which the N-terminal domain and the C terminus of the HBV core protein form two distinct and structurally independent entities. The strong tendency of the N-terminal domain for dimeric interactions suggests that core protein dimers are the major intermediates in hepatitis B virus nucleocapsid assembly.
J Mol Biol 1992 Jun 20
PMID:Topological analysis of the hepatitis B virus core particle by cysteine-cysteine cross-linking. 161 86

Small, defined in-frame deletions and in-frame duplications of specific sequences were made within the faeG gene encoding the K88ab fimbrial subunit protein from porcine enterotoxigenic Escherichia coli. The cellular localization and proteolytic stability of the different mutated fimbrial subunit proteins were determined, and compared with those of the wild-type protein. Based upon these results, we predict a functional role of specific structures in the K88ab fimbrial subunit protein in subunit-subunit interactions as well as in interactions between FaeG and the other proteins encoded by the K88ab operon. The results obtained were further compared with results obtained from operon deletions, linker insertion mutagenesis and the current model for biogenesis of K88 fimbriae. One of the mutated fimbrial subunit genes was used to construct a secreted in-frame fusion between FaeG and a characterized epitope (lacking cysteine) from the Hepatitis B pre-S2 protein. Such fusion proteins might be useful in the design of recombinant vaccines.
Mol Gen Genet 1991 Oct
PMID:Deletion and duplication of specific sequences in the K88ab fimbrial subunit protein from porcine enterotoxigenic Escherichia coli. 168 14

We studied the effects of transfection of the normal c-Ha-ras gene, rasGly-12, and its oncogenic mutant, rasVal-12, on expression of the alpha-fetoprotein (AFP) and albumin genes in a human hepatoma cell line, HuH-7. The mutant and, to a lesser extent, the normal ras gene caused reduction of the AFP mRNA but not the albumin mRNA level in transfected HuH-7 cells. Cotransfection experiments with a rasVal-12 expression plasmid and a chloramphenicol acetyltransferase reporter gene fused to AFP regulatory sequences showed that rasVal-12 suppressed the activity of enhancer and promoter regions containing A + T-rich sequences (AT motif). In contrast, rasVal-12 did not affect the promoter activity of the albumin and human hepatitis B virus pre-S1 genes even though these promoters contain homologous A + T-rich elements. ras transfection appeared to induce phosphorylation of nuclear proteins that interact with the AFP AT motif, since gel mobility analysis revealed the formation of slow-moving complexes which was reversed by phosphatase treatment. However, similar changes in complex formation were observed with the albumin and hepatitis B surface antigen pre-S1 promoters. Therefore, this effect alone cannot explain the specific down regulation of the AFP promoter and enhancer activity. ras-mediated suppression of the AFP gene may reflect the process of developmental gene regulation in which AFP gene transcription is controlled by a G-protein-linked signal transduction cascade triggered by external growth stimuli.
Mol Cell Biol 1990 Apr
PMID:c-Ha-ras down regulates the alpha-fetoprotein gene but not the albumin gene in human hepatoma cells. 169 Aug 41

Hepatitis B surface antigen (HBsAg) particles carry the common determinant, a, as well as d or y and w or r subtype determinants, and are classified into the four major subtypes, i.e., adw, adr, ayw and ayr. Rare sera contain HBsAg particles with all four subtype determinants (adywr). Target sequences (nucleotides 38-550) in the S gene of hepatitis B virus (HBV) DNA in two such sera were amplified by the polymerase chain reaction. Individual amplification products were cloned in an M13 phage vector. The HBV DNA clones obtained were subtyped by determining the second letters of codon 122 and 160 for lysine (AAA/AAG) or arginine (AGA/AGG), which specify the d or y and w or r determinants, respectively. From one serum (S-63), two adw, 10 adr and 58 ayr clones were obtained. When the two adw clones and two representatives each of the adr and ayr clones were compared against each other, for the sequence of 235 base pairs representing nucleotides 295-529 in the S gene, they differed only by 0.4-2.1% (average 1.2%). These results indicated multiple point mutations of a single HBV strain of subtype ayr and co-infection of hepatocytes with the original HBV strain and its mutant of subtype adw as the mechanism for the production of HBsAg/adywr particles. From the other serum (K-45), 1 adw, 73 adr and 4 ayw clones were obtained. The adw clone and two representative adr clones differed only by 0-1.7% in the S gene sequences, but they differed by 8.5% or greater from two representative ayw clones. HBsAg/adywr particles in this serum, therefore, could be explained by double infection of hepatocytes with two HBV strains of different subtypes (adr and ayw).
Mol Immunol 1990 May
PMID:Hepatitis B surface antigen particles with all four subtypic determinants: point mutations of hepatitis B virus DNA inducing phenotypic changes or double infection with viruses of different subtypes. 169 59

The complete amino acid (aa) sequence of the hepatitis B virus (HBV) core protein (HBcAg), deduced from the genome of the HBV ayw subtype, was synthesized as decapeptides with five overlapping aas. The peptides were tested for reactivity with monoclonal antibodies (mAbs) to the beta (or HBe2) epitope of hepatitis B e antigen (HBe/b mAbs; 57/8, 78/3, 141/158 and 141/207). Cross-competition between the mAbs with a mAb to the HBe/alpha epitope (or HBe1) and an anti-HBc mAb showed that all the HBe/b mAbs specifically inhibited human anti-HBe/b binding. Screening the HBc/e peptides showed that all anti-HBe/b mAbs recognized a peptide covering the residues 126-135. Three of the mAbs, 78/3, 141/152 and 141/207, had a less restricted reactivity than the other two, suggesting the recognition of the HBe/b as a discontinuous determinant. Fine mapping of the region aa 126-135 was performed by synthesizing decapeptides with nine overlapping aas, covering residues aa 121-140. All mAbs, except 78/3, reacted with the linear sequence TPPAYR, at residues 128-133. An additional set of peptides was synthesized, where the six aas within the epitope 128-133 were substituted in turn by the other 19 possible aas. By this approach, the essential aas for mAb 57/8 were found to be the sequence of PPA at residues 129-131, and for mAb 141/158 the sequence PP-Y, at residues 129, 130 and 132, respectively. Human recognition of the linear HBe/b epitope was investigated by using a peptide covering residues 121-140 (p 33). Thirty-one sera from chronic carriers of HBsAg, of which seven were positive for HBeAg and the remaining 24 for anti-HBe, were investigated. Of the sera with HBeAg, two had low levels of anti/-HBe/b in the p 33 assay. Out of the sera with anti-HBe, eight were positive in the p 33 EIA. Thus, murine monoclonals and human sera may recognize the HBe/b epitope as a linear determinant residing around aa 130.
Mol Immunol 1991 Jul
PMID:Human and murine B-cells recognize the HBeAg/beta (or HBe2) epitope as a linear determinant. 171 95

Insertion of 48 amino acid long sequence of envelope protein gp51 of bovine leukemia virus (BLV), located from position 56 till 103 of mature protein, into Pro144 position of hepatitis B core antigen (HBcAg) leads to the formation of chimeric capsids. These capsids preserve morphology of intact HBcAg but expose on their outer surface BLV epitopes which are localised in the inserted gp51 fragment and responsible for the recognition of chimeras by monoclonal anti-gp51 antibodies MAK14. The anti-genicity of gp51 epitopes within chimeric capsids is not disturbed after shortening of C terminal part of inserted gp51 fragment by deletion of amino acids 73-103. The resulting chimeras show the same capsid-forming ability as well as HBcAg and gp51 antigenic properties.
Mol Biol (Mosk)
PMID:[Exposure of the major immunodominant epitope of the gp51 envelope protein of bovine leukosis virus on the surface of the hepatitis B core antigen capsid]. 171 9


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