Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019158 (hepatitis)
 30,205 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To examine the role of hepatitis delta virus antigen in the replication of hepatitis delta virus RNA, we have transfected a stable HDAg-positive cell line (A3) and the parental HDAg-negative line (HepG2) with HDV RNA produced in vitro; synthesis of complementary HDV RNA was only detected in HDAg-positive cultures. In contrast, nuclear homogenates from both HDAg-positive and -negative cells synthesized comparable levels of complementary RNA from exogenous HDV RNA. These findings indicate that HDAg is not a necessary component of the transcriptional complex and suggest with other evidence, that a major role for HDAg is likely to be transport of HDV RNA from cytoplasm to nucleus. Transcription of HDV RNA by intact nuclei was sensitive to 1 microgram/ml alpha-amanatin providing firm evidence that, like viroids, this function is performed by host RNA polymerase II.
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PMID:Hepatitis delta antigen is necessary for access of hepatitis delta virus RNA to the cell transcriptional machinery but is not part of the transcriptional complex. 165 99

Hepatitis delta virus (HDV) contains a circular, viroid-like RNA genome, the only animal viral RNA of its kind. It possesses a ribozyme activity, which can autocatalytically cleave and ligate itself. The ribozyme has a unique structural requirement different from other known ribozymes. HDV RNA undergoes RNA-dependent RNA replication via a double rolling circle mechanism, which is probably mediated by cellular RNA polymerase II, utilizing modified cellular transcription machineries. HDV RNA encodes a single protein, hepatitis delta antigen, which is a nuclear, RNA-binding phosphoprotein and required for viral RNA replication. During replication, HDV RNA undergoes a specific RNA editing event to extend its open reading frame and produce a longer, isoprenylated delta antigen, which suppresses RNA replication and initiates viral particle assembly. Ribozyme, cell-mediated RNA-dependent RNA replication, and RNA editing are some of the unique properties and unresolved issues of the molecular biology of HDV.
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PMID:The molecular biology of hepatitis delta virus. 757 82

Human hepatitis delta virus has a single-stranded circular RNA genome that replicates by RNA-directed RNA synthesis. The virus encodes only a single protein, the delta antigen, which both is small (22 kDa) and lacks sequence homology to known RNA polymerases, suggesting that the virus employs a cellular polymerase for replication. Consistent with this suggestion, we have used homogenized nuclei from a human hepatoma cell line, HepG2, to demonstrate RNA-directed RNA synthesis from both genomic hepatitis delta virus RNA and its complement, the antigenomic RNA. RNA polymerase II was responsible for this transcription because the reaction was inhibited both by low doses of alpha-amanitin and by a monoclonal antibody specific for polymerase II. In addition, it was found that the majority of the RNA products were processed, presumably by self-cleavage and self-ligation, to produce covalently closed circular molecules.
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PMID:The RNAs of hepatitis delta virus are copied by RNA polymerase II in nuclear homogenates. 823 Apr 19

Transcription and replication of hepatitis delta virus (HDV) RNA is thought to be performed by host RNA polymerase II. The mechanism which enables polymerase II to use RNA as a template is unclear. However, since extensive intramolecular complementarity allows HDV RNA to form a rod-shaped structure, it is possible that the mostly double-stranded HDV RNA may resemble double-stranded DNA in structure, and can thus be used by RNA polymerase II as a template. To investigate this possibility, we examined whether the cDNA counterpart of HDV RNA contains a promoter and thus can drive the transcription and replication of HDV RNA. Circularized monomers of HDV cDNA, when transfected into various cell lines, were found to generate both monomeric and dimeric forms of HDV RNA and hepatitis delta antigen at levels comparable to those generated with HDV cDNA multimers under the control of a SV40 late promoter, suggesting that HDV cDNA contains endogenous promoters. Using chloramphenicol acetyltransferase and human growth hormone as reporter genes, the specific promoter activity for the synthesis of antigenomic HDV RNA was localized to a 29-nucleotide region (nucleotides 1650-1679), although an additional 224-nucleotide upstream region was also necessary for maximum activity. Similarly, promoter activity for the synthesis of genomic RNA was localized to a 160-nucleotide region around position 1679 that overlapped with the antigenomic promoter region. Since these regions are in a highly conserved double-stranded region of HDV RNA, they may represent RNA promoters recognized by RNA polymerase II. This result also suggests a convenient method, using circularized monomer HDV cDNA, to study HDV RNA replication.
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PMID:Endogenous promoters can direct the transcription of hepatitis delta virus RNA from a recircularized cDNA template. 837 36

Transcription and replication of hepatitis delta virus (HDV) RNA are performed by the cellular enzyme RNA polymerase II (Pol II). As DNA is the normal template for Pol II, the enzyme must undergo template switching. The mechanism for this is unknown, but since HDV RNA can form a rod-like molecule by extensive intramolecular base pairing, it has been suggested that a double-stranded region(s) of HDV RNA serves as a recognition site for Pol II. A bidirectional promoter has been identified previously on HDV cDNA (T. B. Macnaughton, M. R. Beard, M. Chao, E. J. Gowans, and M. M. C. Lai, Virology 196:629-636, 1993). In the present study, genomic RNA corresponding to this region was able to direct the synthesis of antigenomic RNA in a nuclear extract transcription reaction, whereas genomic RNA species containing a mutation that resulted in a replication-defective phenotype were unable to do so. Thus, this region, the location of which is defined as nucleotides 1608 to 1669 on the basis of a highly conserved structure, represents a RNA-RNA promoter. Computer analysis of the RNA secondary structure predicted that the promoter contains two bulge regions in a stem-loop structure which encompasses a GC-rich motif. This predicted model was confirmed by enzyme digestion and primer extension analysis. The promoter is located at one end of the rod and has some homology with the simian virus 40 late promoter. A number of other mutations were introduced within this region, and expression plasmids were constructed to examine the effects of mutations in the promoter on HDV replication. Disruption of the overall secondary structure, particularly the bulge regions, totally inhibited HDV RNA replication.
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PMID:Identification and characterization of a hepatitis delta virus RNA transcriptional promoter. 876 5

After the discovery of HDV there have been significant advances in the understanding of the biology and disease of HDV infection. Analyses at the molecular level have revealed several fascinating features (ribozyme activity, RNA-dependent RNA polymerase activity of RNA polymerase II, HDAg isoprenylation, and RNA editing) that are of significant interest. Intensive investigation of the ribozyme elements has yielded important insights in both functional and structural features. However, there is information lacking about other aspects of the HDV replication cycle including the specific nature of the interaction between HDAg and HDV RNA, the function of HDAg in HDV RNA replication, transcription by RNA polymerase II, and the mechanisms of HDV RNA editing and its regulation. Further study of these and other aspects of the HDV replication cycle will continue to enrich our understanding of basic biology. Evaluation of the mechanisms of HDV disease remains an important goal in the study of this agent. Although both acute and chronic disease are commonly associated with unfavorable outcomes, it is clear that chronic infection is associated with a broad spectrum of disease. The interactions between HDV, HBV, and the host are necessarily complex, and it is likely that each contribute factors that influence disease and outcome. Recent analyses of HDV genotypes have suggested that disease variations may be associated with viral genetic factors. Consistent with the obligate role of HBV in the HDV life cycle, HBV replication is also an important determinant of HDV disease. It is still unclear if interactions between specific genotypes or variants of HBV and HDV influence disease. Recent data also suggest that infection with multiple hepatitis viruses (HBV, HDV, and HCV) can influence the severity of disease. It remains to be seen whether coinfection with the recently discovered hepatitis G virus is associated with altered disease patterns. Further advances in our understanding HDV disease and possible therapeutic approaches will rely on a combination of additional studies at the molecular, genetic, epidemiologic, and clinical levels. These studies will continue to elaborate the model of HDV infection and disease that can ultimately be tested by experimental infection of chimpanzees and woodchucks.
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PMID:Hepatitis delta virus. Genetics and pathogenesis. 879 82

When the small form of the delta antigen (deltaAg-S) was expressed from a cDNA expression plasmid and subsequently detected by immunofluorescence, it was found localized to the nucleoli. However, if the cDNA was cotransfected with a cDNA expressing a mutated hepatitis delta virus (HDV) genome that could only replicate by using the deltaAg-S provided by the first plasmid, then most of the deltaAg-S was redistributed to the nucleoplasm, largely to specific discrete nucleoplasmic sites or speckles; this pattern was stable for at least 50 days after transfection. These speckles coincided with those detected with an antibody to SC35, an essential non-small nuclear ribonucleoprotein splicing factor. Others have shown that SC35 speckles correspond to active sites of DNA-directed transcription by RNA polymerase II and also of RNA processing. We also found, in contrast to the cotransfections with the mutant HDV and the deltaAg-S provided in trans, that cells transfected with wild-type HDV showed a variable pattern of staining. The SC35-like speckle pattern of accumulation of delta antigen deltaAg was maintained for only 6 days, after which the pattern began to change. By 18 days posttransfection, a variety of different deltaAg staining patterns were observed. This pattern of change occurs at a time when the large form of the delta antigen deltaAg-L appears and HDV RNA synthesis begins to shut down. Our studies therefore support the interpretation that HDV RNA and deltaAg-S accumulate at SC35 speckle sites in the nucleoplasm. We speculate that these may be the sites at which HDV RNA is transcribed by RNA polymerase II and/or sites of HDV RNA processing. Furthermore, when deltaAg-L, as well as other mutant deltaAg accumulate, the speckle association is disrupted, thereby stopping HDV RNA replication.
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PMID:Redistribution of the delta antigens in cells replicating the genome of hepatitis delta virus. 889 31

To develop vector systems that combine high transcription activity with biologically safe delivery vehicles, we have explored the use of RNA replication to amplify mRNAs, by using flock house virus (FHV) as a model system. The FHV RNA replicase is encoded in the larger of the two segments that comprise the viral positive-sense RNA genome. A cDNA copy of this self-replicating RNA was precisely positioned between a promoter site for cellular RNA polymerase II and a cDNA encoding a self-cleaving ribozyme from hepatitis delta virus. Transfection of this plasmid into cultured BHK cells resulted in prolonged, autonomous FHV RNA replication in the cytoplasm and substantial amplification of the RNA replicon. The replicase also amplified RNA transcribed from a second plasmid of similar design that contained a cDNA copy of the other FHV genome segment. These results constitute a significant step toward the harnessing of nodaviral RNA replication as the basis of a versatile vector system.
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PMID:Replication of flock house virus RNAs from primary transcripts made in cells by RNA polymerase II. 906 Jul 3

RNA polymerase II is implicated in the RNA-templated RNA synthesis during replication of viroids and Hepatitis Delta Virus (HDV); however, neither the RNA template nor protein factor requirements for this process are well defined. We have developed an in vitro transcription system based on HeLa cell nuclear extract (NE), in which a segment of antigenomic RNA corresponding to the left-hand tip region of the HDV rod-like structure serves as a template for efficient and highly specific RNA synthesis. Accumulation of the unique RNA product is highly sensitive to alpha-amanitin in HeLa NE and only partially sensitive to this drug in NE from PMG cells that contain an allele of the alpha-amanitin-resistant subunit of pol II, strongly suggesting pol II involvement in this reaction. Detailed analysis of the RNA product revealed that it represents a chimeric molecule composed of a newly synthesized transcript covalently attached to the 5' half of the RNA template. Selection of the start site for transcription is remarkably specific and depends on the secondary structure of the RNA template, rather than on its primary sequence. Some features of this reaction resemble the RNA cleavage-extension process observed for pol II-arrested complexes in vitro. A possible involvement of the described reaction in HDV replication is discussed.
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PMID:Specific HDV RNA-templated transcription by pol II in vitro. 1066 97

Replication of hepatitis delta virus (HDV) RNA occurs in the nuclei of infected cells. The replication is mediated by cellular factors containing an RNA polymerase II-like enzyme activity through a double rolling-circle mechanism and is regulated by delta antigens. In this study, UV cross-linking experiments were carried out to examine interactions between HDV RNA and proteins present in HeLa nuclear extract. Cellular proteins with molecular mass of 23 (p23), 36 (p36), 38 (p38), and 58 (p58) kDa bound to full-length HDV RNA of both genomic and antigenomic strands. Deletion analysis on the antigenomic strand mapped the interacting domain within a 79-nucleotide fragment but not at the ends of the rod-shaped viral RNA structure. The specificity of the RNA-protein interactions was demonstrated by competition experiments and the specific HDV RNA-binding proteins were purified through column chromatography. Electrophoresis mobility shift assay with the purified fractions demonstrated that the interaction between p36 and HDV RNA was relatively stable even in the presence of 0.5 M NaCl. Biochemical analysis including protein microsequencing identified the p36 as glyceraldehyde 3-phosphate dehydrogenase (GAPDH). RNase footprinting indicated that the UC-rich domain between nucleotides 379 and 414 of the HDV antigenomic RNA was involved in the GAPDH binding. Functional studies further demonstrated an enhancing effect of GAPDH on the ribozyme activity of HDV antigenomic RNA. In addition, in the presence of HDV RNA cellular GAPDH relocalized from the cytoplasm to the nucleus where HDV replication occurs. These results suggest that GAPDH is involved in the replication of HDV.
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PMID:Specific interaction between the hepatitis delta virus RNA and glyceraldehyde 3-phosphate dehydrogenase: an enhancement on ribozyme catalysis. 1081 69


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