Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.48 (transcriptase)
9,479 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, causes an acute infection of the central nervous system resulting in encephalitis of humans and many kinds of animals. NS5, the largest and most conserved flavivirus protein, is homologous to methyltransferase and RNA-dependent RNA polymerase. RNA interference is an effective anti-viral strategy to inhibit viral replication in vitro. In this study, four short hairpin RNA (shRNA) expression vectors (pS4.1-NS5-201, pS4.1-NS5-455, pS4.1-NS5-699, and pS4.1-NS5-804) targeting the NS5 gene of JEV were employed to target and destroy JEV transcripts. The four shRNAs expression plasmids were individually co-transfected into 293T cells with the plasmid pNS5-EGFP expressing NS5 fused to enhanced green fluorescent protein. The expression level of NS5 was evaluated by fluorescence microscopy, flow cytometry, real time RT-PCR, and Western blot. The four shRNA expression plasmids were also transfected into BHK-21 cells to examine their inhibition of viral replication by indirect immunofluorescence, real time RT-PCR, and Western blot. The results provided strong evidence that shRNAs targeting the NS5 gene could specifically and efficiently inhibit JEV replication. Three out of four plasmids were highly efficient at inhibiting viral replication, including pS4.1-NS5-455, pS4.1-NS5-699, and pS4.1-NS5-804. This was especially true for pS4.1-NS5-699, which reduced the levels of virus RNA and protein the most. Our data suggest that shRNAs could be used as a tool to inhibit JEV replication in vivo.
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PMID:Effective inhibition of Japanese encephalitis virus replication by small interfering RNAs targeting the NS5 gene. 1819 Sep 94

Flavivirus methyltransferase catalyzes both guanine N7 and ribose 2'-OH methylations of the viral RNA cap (GpppA-RNA-->m(7)GpppAm-RNA). The methyltransferase is physically linked to an RNA-dependent RNA polymerase (RdRp) in the flaviviral NS5 protein. Here, we report genetic interactions of West Nile virus (WNV) methyltransferase with the RdRp and the 5'-terminal stem-loop of viral genomic RNA. Genome-length RNAs, containing amino acid substitutions of D146 (a residue essential for both cap methylations) in the methyltransferase, were transfected into BHK-21 cells. Among the four mutant RNAs (D146L, D146P, D146R, and D146S), only D146S RNA generated viruses in transfected cells. Sequencing of the recovered viruses revealed that, besides the D146S change in the methyltransferase, two classes of compensatory mutations had reproducibly emerged. Class 1 mutations were located in the 5'-terminal stem-loop of the genomic RNA (a G35U substitution or U38 insertion). Class 2 mutations resided in NS5 (K61Q in methyltransferase and W751R in RdRp). Mutagenesis analysis, using a genome-length RNA and a replicon of WNV, demonstrated that the D146S substitution alone was lethal for viral replication; however, the compensatory mutations rescued replication, with the highest rescuing efficiency occurring when both classes of mutations were present. Biochemical analysis showed that a low level of N7 methylation of the D146S methyltransferase is essential for the recovery of adaptive viruses. The methyltransferase K61Q mutation facilitates viral replication through improved N7 methylation activity. The RdRp W751R mutation improves viral replication through an enhanced polymerase activity. Our results have clearly established genetic interactions among flaviviral methyltransferase, RdRp, and the 5' stem-loop of the genomic RNA.
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PMID:Genetic interactions among the West Nile virus methyltransferase, the RNA-dependent RNA polymerase, and the 5' stem-loop of genomic RNA. 1844 28

Flaviviruses are a major cause of infectious disease in humans. Dengue virus causes an estimated 50 million cases of febrile illness each year, including an increasing number of cases of hemorrhagic fever. West Nile virus, which recently spread from the Mediterranean basin to the Western Hemisphere, now causes thousands of sporadic cases of encephalitis annually. Despite the existence of licensed vaccines, yellow fever, Japanese encephalitis and tick-borne encephalitis also claim many thousands of victims each year across their vast endemic areas. Antiviral therapy could potentially reduce morbidity and mortality from flavivirus infections, but no effective drugs are currently available. This article introduces a collection of papers in Antiviral Research on molecular targets for flavivirus antiviral drug design and murine models of dengue virus disease that aims to encourage drug development efforts. After reviewing the flavivirus replication cycle, we discuss the envelope glycoprotein, NS3 protease, NS3 helicase, NS5 methyltransferase and NS5 RNA-dependent RNA polymerase as potential drug targets, with special attention being given to the viral protease. The other viral proteins are the subject of individual articles in the journal. Together, these papers highlight current status of drug discovery efforts for flavivirus diseases and suggest promising areas for further research.
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PMID:Molecular targets for flavivirus drug discovery. 1879 13

West Nile virus (WNV) is a member of the Flaviviridae family which includes a number of important human pathogens. The WNV NS5 protein harbors an RNA-dependent RNA polymerase activity which is required both for replication and transcription of the viral genome. To extend our studies on the role of metal ions in the activity of flaviviral polymerases, we have used fluorescence spectroscopy, circular dichroism, and a combination of chemical and thermal denaturation assays to monitor the consequences of metal ion binding to the enzyme. We demonstrate that the binding of magnesium is not critical for the structural stabilization of the enzyme. Moreover, structural studies indicate that the protein does not undergo conformational change upon the binding of magnesium ions. Additional binding assays also indicate that the interaction of magnesium ions with the enzyme does not significantly stimulate the interaction with the RNA or NTP substrates. The inability of cobalt hexamine, an exchange-inert metal complex structurally analogous to magnesium hexahydrate, to support the catalytic activity also allowed us to demonstrate a direct role of magnesium ions in the catalytic activity of the enzyme. Finally, a three-dimensional structural model of the active center of the enzyme was generated which highlighted the importance of two aspartate residues involved in the coordination of two metal ions. Mutational analyses confirmed the importance of these two amino acids for the binding of magnesium ions. Our data provide further insight into the precise role of magnesium ions for the RNA polymerase activity of the protein, and more importantly, highlight key differences between the RNA polymerases of the Flaviviridae family.
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PMID:Metal ion-binding studies highlight important differences between flaviviral RNA polymerases. 1893 Aug 44

Replication of the Japanese encephalitis virus (JEV) genome depends on host factors for successfully completing their life cycles; to do this, host factors have been recruited and/or relocated to the site of viral replication. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a cellular metabolic protein, was found to colocalize with viral RNA-dependent RNA polymerase (NS5) in JEV-infected cells. Subcellular fractionation further indicated that GAPDH remained relatively constant in the cytosol, while increasing at 12 to 24 hours postinfection (hpi) and decreasing at 36 hpi in the nuclear fraction of infected cells. In contrast, the redistribution patterns of GAPDH were not observed in the uninfected cells. Co-immunoprecipitation of GAPDH and JEV NS5 protein revealed no direct protein-protein interaction; instead, GAPDH binds to the 3' termini of plus- and minus-strand RNAs of JEV by electrophoretic mobility shift assays. Accordingly, GAPDH binds to the minus strand more efficiently than to the plus strand of JEV RNAs. This study highlights the findings that infection of JEV changes subcellular localization of GAPDH suggesting that this metabolic enzyme may play a role in JEV replication.
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PMID:Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) interaction with 3' ends of Japanese encephalitis virus RNA and colocalization with the viral NS5 protein. 1936 2

The West Nile virus (WNV) NS5 protein contains a methyltransferase (MTase) domain involved in RNA capping and an RNA-dependent RNA polymerase (RdRp) domain essential for virus replication. Crystal structures of individual WNV MTase and RdRp domains have been solved; however, the structure of full-length NS5 has not been determined. To gain more insight into the structure of NS5 and interactions between the MTase and RdRp domains, we generated a panel of seven monoclonal antibodies (mAbs) to the NS5 protein of WNV (Kunjin strain) and mapped their binding sites using a series of truncated NS5 proteins and synthetic peptides. Binding sites of four mAbs (5D4, 4B6, 5C11 and 6A10) were mapped to residues 354-389 in the fingers subdomain of the RdRp. This is consistent with the ability of these mAbs to inhibit RdRp activity in vitro and suggests that this region represents a potential target for RdRp inhibitors. Using a series of synthetic peptides, we also identified a linear epitope (bound by mAb 5H1) that mapped to a 13 aa stretch surrounding residues 47 and 49 in the MTase domain, a region predicted to interact with the palm subdomain of the RdRp. The failure of one mAb (7G6) to bind both N- and C-terminally truncated NS5 recombinants indicates that the antibody recognizes a conformational epitope that requires the presence of residues in both the MTase and RdRp domains. These data support a structural model of the full-length NS5 molecule that predicts a physical interaction between the MTase and the RdRp domains.
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PMID:Monoclonal antibodies to the West Nile virus NS5 protein map to linear and conformational epitopes in the methyltransferase and polymerase domains. 1971 Feb 54

NS3 of pestiviruses contains a protease domain and a RNA helicase/NTPase domain. Contradictory results have been reported regarding NS3 in RNA synthesis. To investigate the effect of NS3 on classical swine fever virus (CSFV) NS5B RNA-dependent RNA polymerase activity (RdRp) activity and NS3-NS5B interaction, RdRp reactions, GST-pull-down assays and co-immunoprecipitation analyses containing NS5B and either of NS3 protein and the different truncated NS3 mutants were performed, respectively. We found that NS3 stimulated NS5B RdRp activity in a dose-dependent manner by binding to NS5 through a NS3 protease domain. Furthermore, mapping important regions of the NS3 protease domain was carried out by deletion mutagenesis, associated with RdRp reactions, GST-pull-down assays and co-immunoprecipitation analyses. Results showed that stimulation of CSFV NS5B RdRp activity was obtained by NS3 binding to NS5B through a 31-amino acid fragment at the N-terminal end of NS3 protease domain, which mediated a specific NS3-NS5B interaction.
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PMID:Classical swine fever virus NS3 enhances RNA-dependent RNA polymerase activity by binding to NS5B. 1995 25

RNA elements within the flavivirus genome may play essential regulatory roles during virus replication. Here, recombinant West Nile virus (WNV) NS5 protein was used in combination with WNV subgenomic RNA templates to establish in vitro RNA-dependent RNA polymerase and RNA-binding assays. These assays identified mutations in the stem-loop A (SLA) region of the 5' untranslated region (5'UTR) altering NS5 RNA synthesis and RNA-binding capability. These mutations were then introduced into the full-length WNV genome by reverse genetics. Further analysis of the mutant viruses showed that deletion of nt 46-60, which disrupted the stem and side loop of SLA, greatly compromised virus replication, whereas mutations that destroyed the top loop of SLA required for RNA synthesis in vitro did not significantly alter virus replication. These results suggest that SLA present in the 5'UTR of WNV is essential for RNA synthesis in vitro and for virus replication.
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PMID:RNA elements within the 5' untranslated region of the West Nile virus genome are critical for RNA synthesis and virus replication. 2001 34

Dengue virus (DENV) is the most prevalent mosquito-borne viral pathogen in humans. Neither vaccine nor antiviral therapy is currently available for DENV. We report here that N-sulfonylanthranilic acid derivatives are allosteric inhibitors of DENV RNA-dependent RNA polymerase (RdRp). The inhibitor was identified through high-throughput screening of one million compounds using a primer extension-based RdRp assay [substrate poly(C)/oligo(G)(20)]. Chemical modification of the initial "hit" improved the compound potency to an IC(50) (that is, a concentration that inhibits 50% RdRp activity) of 0.7 microM. In addition to suppressing the primer extension-based RNA elongation, the compound also inhibited de novo RNA synthesis using a DENV subgenomic RNA, but at a lower potency (IC(50) of 5 microM). Remarkably, the observed anti-polymerase activity is specific to DENV RdRp; the compound did not inhibit WNV RdRp and exhibited IC(50)s of >100 microM against hepatitis C virus RdRp and human DNA polymerase alpha and beta. UV cross-linking and mass spectrometric analysis showed that a photoreactive inhibitor could be cross-linked to Met343 within the RdRp domain of DENV NS5. On the crystal structure of DENV RdRp, Met343 is located at the entrance of RNA template tunnel. Biochemical experiments showed that the order of addition of RNA template and inhibitor during the assembly of RdRp reaction affected compound potency. Collectively, the results indicate that the compound inhibits RdRp through blocking the RNA tunnel. This study has provided direct evidence to support the hypothesis that allosteric pockets from flavivirus RdRp could be targeted for antiviral development.
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PMID:Inhibition of dengue virus polymerase by blocking of the RNA tunnel. 2023 86

Outbreaks of West Nile virus (WNV) have occurred intermittently in regions around the Mediterranean coast, and the virus may have become established in Northern Italy and Romania, with reported intermittent outbreaks in Spain, Hungary, and France. WNV has also spread rapidly throughout the Americas since its introduction into New York in 1999. This capacity to emerge in new geographical locations and to spread rapidly together with the current increase in incidence of other flaviviruses such as tick-borne encephalitis virus, dengue virus, and Usutu virus has prompted us to design a novel pan-flavivirus RT-polymerase chain reaction for the purpose of surveillance for a range of flaviviruses. The assay utilizes degenerate primers targeting the flavivirus NS5 gene (RNA-dependent RNA polymerase) and detects a range of flaviviruses, including WNV. A small panel of WNV bird samples obtained from the United States has been shown to be detected using this assay. The amplicon generated is of sufficient size to provide sequence data to confirm the identity of the virus detected and undertake limited phylogenetic analysis. Testing using this assay has shown its ability to detect a range of tick-borne flaviviruses, particularly louping ill virus that is endemic in areas of the United Kingdom. The assay has been used to survey 160 bird samples and 1000 mosquito samples from the United Kingdom and found no evidence for WNV.
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PMID:Assessment of a novel real-time pan-flavivirus RT-polymerase chain reaction. 2085 19


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