Studying HCV RNA synthesis in vitro with replication complexes.

HCV replication complexes are well-organized protein and lipid structures responsible for HCV RNA replication. The nonstructural protein NS5B, an RNA-dependent RNA polymerase, is the catalytic subunit of these replication complexes. After being isolated from HCV replicon-containing cells as a crude membrane fraction, these replication complexes have been shown to remain active in synthesis of viral RNA under proper assay conditions. Under the improved assay conditions presented here, we recently showed that isolated replication complexes are able to synthesize two species of nascent viral RNA, one double stranded and the other single stranded. NS5B nucleoside inhibitors block synthesis of both species, whereas nonnucleoside inhibitors inhibit mostly single- tranded RNA synthesis. Our results support the discoveries with recombinant NS5B biochemical assay that nucleoside inhibitors and nonnucleoside inhibitors block viral RNA synthesis by different mechanisms.