Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.48 (transcriptase)
 9,479 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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

Recently, new blood-transfusion transmissible viruses, called hepatitis G virus(HGV) and GB virus-C(GBV-C), have been reported. It was found that two viruses were independent isolates of the same virus, the genomic structure resembled that of flavivirus family, and GBV-C/HGV was closely related to HCV. To elucidate the evolutionary relationship between hepatitis C virus(HCV) and GBV-C/HGV, we constructed the phylogenetic trees for the putative RNA helicase and the RNA-dependent RNA polymerase regions of the Flaviviridae by UPGMA. The tree showed that HCV was closely related to GB virus-B(GBV-B) and HGV was more nearer to GB virus-A(GBV-A) rather than HCV.
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PMID:[Molecular evolutionary analysis of GB viruses and hepatitis G virus]. 908 54

A recently discovered non-A-E hepatitis virus has been designated as hepatitis G virus (HGV) and identified as a new member of the Flaviviridae family. Infection by this virus is thought to be associated with blood-borne hepatitis and usually in the presence of hepatitis C or hepatitis B virus (HBV) infection. In this study, the presence of HGV-RNA in serum or plasma and the prevalence of antibodies against an HGV envelope protein (E2) were investigated in patients undergoing chronic hemodialysis using a sensitive reverse-transcriptase polymerase chain reaction and an enzyme-linked immunosorbent assay, respectively. HGV-RNA was detected in 19 of 112 patients investigated (17%) and anti-E2 antibodies were detected in 15 of 106 patients studied (14.2%). With the exception of two patients, the appearance of anti-E2 is associated with the clearance of serum HGV-RNA. The total prevalence of current (HGV-RNA positivity) and/or past (anti-E2 positivity) HGV infection in this patient population is thus 28.6% (32 of 112 patients were positive for serum HGV-RNA and/or anti-E2 antibodies). In apparently healthy blood donors, serum HGV-RNA was detected in four of 358 individuals (1.12%) and anti-E2 was not detected in 50 individuals investigated. From the 19 patients with serum HGV-RNA positivity, nine were coinfected with other hepatitis viruses (seven with HBV; one with HBV, hepatitis C virus [HCV], and hepatitis D virus; and one with HBV and cytomegalovirus). Thirteen of 15 patients with anti-E2 positivity (10 were positive for only anti-E2 and three were also positive for anti-HBc) had no detectable HGV-RNA. In two patients, both HGV-RNA and anti-E2 antibodies were concomitantly present (both patients were coinfected with HCV or HBV). Of the HGV-infected patients, only three who were coinfected with HBV showed elevated serum alanine aminotransferase levels. The serum HCV-RNA and/or anti-HCV were detected in five (4.5%) of 112 patients. From these findings, we conclude that there is a high prevalence of HGV infection (28.6%) compared with HCV (4.5%) in patients undergoing hemodialysis in our hospital. However, approximately 50% of patients had spontaneously lost the viremia and developed anti-HGV-E2 antibodies. We confirm that HGV infection alone is not associated with elevated serum transaminases, and the appearance of anti-HGV-E2 is usually accompanied with clearance of serum HGV-RNA. In contrast to the results of our previous study, the majority of patients infected with HGV are not coinfected with HCV, indicating that HGV is capable of independent transmission. It is likely that there is a preferential HGV acquisition in the hemodialysis unit. The clinical significance of long-term infection with HGV remains to be established.
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PMID:High prevalence of hepatitis G virus infection compared with hepatitis C virus infection in patients undergoing chronic hemodialysis. 946 14

An RNA virus designated hepatitis G virus (HGV) has been recently identified in patients with acute and chronic liver disease. HGV is transfusion transmissible, it has global distribution, and it is present in the volunteer blood donor population in the United States. One hundred sixty patients undergoing maintenance hemodialysis at the University of Miami-affiliated unit were evaluated. There were 99 men and 61 women ranging in age from 22 to 80 years. Sixty percent had a history of blood transfusion, 6% had a history of drug abuse, and 9% were infected with the human immunodeficiency virus. HGV-RNA was detected by reverse-transcriptase polymerase chain reaction with amplification of two independent regions (5'-nontranslated region and NS5a coding region). Detection of digoxigenin-labeled amplification products with specific capture probes to the coding and noncoding regions was performed with the Enzymun-test DNA on an ES-300 Immunoassay System (Boehringer-Mannheim, Mannheim, Germany). Hepatitis C antibodies were measured with anti-hepatitis C virus enzyme-linked immunosorbent third-generation assays and hepatitis C virus RNA by reverse-transcriptase polymerase chain reaction. There were 32 (20%) patients with detectable HGV RNA with both primer pairs. Because of possible mutations, the HGV virus may be detectable only with one primer pair. We considered the latter as indeterminate: 12 had detectable levels to the NS5a region only, seven to the 5'-nontranslated region, and six had borderline results. Detectable and indeterminate samples were confirmed by repeat measurements in a new blood sample. Seven of 24 (29%) patients with detectable hepatitis C virus RNA had coexisting HGV with one or both HGV primer pairs (four with both and three with one). Five patients were hepatitis B surface antigen positive and HGV negative. We conclude that HGV infection is prevalent in our dialysis patients. The clinical significance of HGV infection remains to be established.
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PMID:Prevalence of hepatitis C and G virus infection in chronic hemodialysis patients. 946 14

The hepatitis G virus (HGV) is a new member of the Flaviviridae family and has a genomic organization similar to that of hepatitis C virus (HCV). Protein sequence motifs are present suggesting that HGV encodes a serine proteinase, an RNA-dependent RNA polymerase and a helicase. We have cloned and expressed the putative helicase of HGV and have shown that it contains a poly (U)-stimulated NTPase activity and is able to function as a DNA helicase. Preliminary characterization of the HGV helicase activity reveals similarities with other members of the Flaviviridae, but especially with HCV, raising the possibility that HGV could be used as a surrogate virus for the development of therapies against HCV.
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PMID:Expression and characterization of the hepatitis G virus helicase. 949 13

Two research groups recently and independently, isolated a hepatotropic flavivirus from human sera. The two viruses, named GB virus C and hepatitis G virus (HGV), were subsequently discovered to represent the same virus, which was associated with acute and chronic hepatitis of the non-A-E type. The prevalences of infection with HGV have now been investigated in various groups of the Thai population, some of which [e.g. thalassaemic children, patients with chronic liver disease, carriers of antibodies to hepatitis B virus and/or hepatitis C virus (HCV), prostitutes and intravenous-drug users (IVDU)] were assumed to be at high risk. Samples of sera were investigated by reverse-transcriptase PCR, using four primers created from the 5' untranslated region of HGV. The prevalence of HGV infection among the healthy controls (1%-5%) was found to be much less than that among thalassaemic children (32.6%), asymptomatic carriers of anti-HCV (20.4%), IVDU (18.2%), aplastic anaemia patients (14.3%) and prostitutes (10%), although similar to that in patients with chronic liver disorders. These results confirm a parenteral route of transmission for HGV and emphasise the need for further research to determine the clinical significance of this virus.
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PMID:Prevalence of infection with hepatitis G virus among various groups in Thailand. 961 58

The family of the Flaviviridae contains 3 genera: (i) the hepaciviruses, to which belongs Hepatitis C virus (HCV), (ii) the flaviviruses and (iii) the pestiviruses. Over 140 million people, more than four times the number of HIV-positive individuals, are chronically infected with the HCV. Hepatitis G virus (HGV) has not yet been assigned to a genus. The impact of this recently discovered virus is yet to be established. Infections with flaviviruses such as Yellow Fever virus (YFV), Dengue Fever virus (DENV), Japanese Encephalitis virus (JEV) and Tick-borne Encephalitis virus (TBEV) are emerging world-wide. The Pestiviruses, Bovine Viral Diarrhea virus (BVDV), Classical Swine Fever virus (CSFV) and Border Disease virus (BDV) have a serious impact on life-stock. At present, only treatment with interferon, alone or combined with ribavirin, has been approved for the treatment of HCV infections. No specific antivirals are available for the treatment of infections with Hepaci-, Flavi- or Pestiviruses. Possible targets for inhibition of the replication of Flaviviridae are the binding to, and the uptake of the virus in the cell; the internal ribosomal entry site (IRES) of Hepaci- and Pestiviruses; viral proteases; the viral RNA-dependent RNA polymerase and the viral helicase. The search for specific inhibitors of HCV replication is hindered by the absence of an efficient cell culture system for propagation of this virus. In addition, small laboratory animals, including mice, are not susceptible to HCV infection. Flaviviruses may cause infection in mice, but do so mainly following direct intracerebral inoculation. We have established a small animal model for flavivirus infections in SCID mice inoculated peripherally with the murine flavivirus Modoc.
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PMID:Infections with flaviviridae. 1065 76

GB virus C/hepatitis G (GBV-C) is an RNA virus of the family Flaviviridae. Despite replicating with an RNA-dependent RNA polymerase, some previous estimates of rates of evolutionary change in GBV-C suggest that it fixes mutations at the anomalously low rate of approximately 10(-7) nucleotide substitution per site, per year. However, these estimates were largely based on the assumption that GBV-C and its close relative GBV-A (New World monkey GB viruses) codiverged with their primate hosts over millions of years. Herein, we estimated the substitution rate of GBV-C using the largest set of dated GBV-C isolates compiled to date and a Bayesian coalescent approach that utilizes the year of sampling and so is independent of the assumption of codivergence. This revealed a rate of evolutionary change approximately four orders of magnitude higher than that estimated previously, in the range of 10(-2) to 10(-3) sub/site/year, and hence in line with those previously determined for RNA viruses in general and the Flaviviridae in particular. In addition, we tested the assumption of host-virus codivergence in GBV-A by performing a reconciliation analysis of host and virus phylogenies. Strikingly, we found no statistical evidence for host-virus codivergence in GBV-A, indicating that substitution rates in the GB viruses should not be estimated from host divergence times.
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PMID:Bayesian coalescent analysis reveals a high rate of molecular evolution in GB virus C. 1832 Feb 58