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NS5B
About: NS5B is a research topic. Over the lifetime, 1314 publications have been published within this topic receiving 59534 citations.
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TL;DR: The virus-encoded RNA-dependent RNA polymerase (RdRp), which is required for replication of the positive-strand RNA genome, is a key enzyme of members of the virus family Flaviviridae and is demonstrated to exhibit a common reactivity profile in vitro, typical of nucleic acid-polymerizing enzymes.
Abstract: The virus-encoded RNA-dependent RNA polymerase (RdRp), which is required for replication of the positive-strand RNA genome, is a key enzyme of members of the virus family Flaviviridae. By using heterologously expressed proteins, we demonstrate that the 77 kDa NS5B protein of two pestiviruses, bovine viral diarrhoea virus and classical swine fever virus, and the 100 kDa NS5 protein of the West Nile flavivirus possess RdRp activity in vitro. As originally shown for the RdRp of hepatitis C virus, RNA synthesis catalysed by the pestivirus and flavivirus enzymes is strictly primer- dependent in vitro. Accordingly, initiation of RNA polymerization on homopolymeric RNAs and heteropolymeric templates, the latter with a blocked 3′-hydroxyl group, was found to be dependent on the presence of complementary oligonucleotide primer molecules. On unblocked heteropolymeric templates, including authentic viral RNAs, the RdRps were shown to initiate RNA synthesis via intramolecular priming at the 3′-hydroxyl group of the template and ‘copy-back’ transcription, thus yielding RNase- resistant hairpin molecules. Taken together, the RdRps of different members of the Flaviviridae were demonstrated to exhibit a common reactivity profile in vitro, typical of nucleic acid- polymerizing enzymes.
112 citations
TL;DR: Results indicate that HCV NS5B initiates RNA synthesis from a single-stranded region closest to the 3′-end of the X region, which has implications for the mechanism ofHCV RNA replication and the nature of HCV RNA templates in the infected cells.
112 citations
TL;DR: It is demonstrated that PSI-6130 is metabolized to two pharmacologically active species in primary human hepatocytes through the formation of 5′-triphosphate and its corresponding phosphorylated metabolites.
112 citations
TL;DR: Preexisting sequence variation could alter the effect of cyclosporine on HCV in vivo, and while both NS5A or NS5B variants alter cyclospora susceptibility, NS5 A has the largest effect.
111 citations
TL;DR: PSI-6130 presents a high barrier to resistance selection in vitro, selects for variants exhibiting only low-level resistance, and lacks cross-resistance with R1479, supporting the continued development of the prodrug R7128 as a therapeutic agent for the treatment of HCV infection.
Abstract: PSI-6130 (β-d-2′-deoxy-2′-fluoro-2′-C-methylcytidine) is a selective inhibitor of hepatitis C virus (HCV) replication that targets the NS5B polymerase. R7128, the prodrug of PSI-6130, has shown antiviral efficacy in patients chronically infected with HCV genotype 1a (GT-1a) and GT-1b. We observed that the compound exhibited potent in vitro activity against laboratory-optimized HCV replicons as well as against a panel of replicons containing NS5B HCV polymerases derived from GT-1a and GT-1b clinical isolates. We used the HCV replicon cell system to examine the emergence of variants with reduced sensitivity to PSI-6130. Short-term treatment of cells harboring the HCV subgenomic replicon with PSI-6130 cleared the replicon without generating resistant variants. Long-term culture of the cells under the compound selection generated the S282T substitution in a complex pattern with other amino acid substitutions in the NS5B polymerase. The presence of the coselected substitutions did not increase the moderate three- to sixfold loss of sensitivity to PSI-6130 mediated by the S282T substitution; however, their presence enhanced the replication capacity compared to the replication levels seen with the S282T substitution alone. We also observed a lack of cross-resistance between PSI-6130 and R1479 and demonstrated that long-term culture selection with PSI-6130 in replicon cells harboring preexisting mutations resistant to R1479 (S96T/N142T) results in the emergence of the S282T substitution and the reversion of S96T to wild-type serine. In conclusion, PSI-6130 presents a high barrier to resistance selection in vitro, selects for variants exhibiting only low-level resistance, and lacks cross-resistance with R1479, supporting the continued development of the prodrug R7128 as a therapeutic agent for the treatment of HCV infection.
111 citations