Promoter/origin structure of the complementary strand of hepatitis C virus genome.

Hepatitis C virus (HCV) NS5B protein encodes an RNA-dependent RNA polymerase (RdRp). Sequences in the 3' termini of both the plus and minus strand of HCV genomic RNA harbor the activity of a replication origin and a transcription promoter. There are unique stem-loop structures in both termini of the viral RNA. We found that the complementary strand of the internal ribosome-binding site (IRES) showed strong template activity in vitro. The complementary strand RNA of the HCV genome works as a template for mRNA and viral genomic RNA. We analyzed the promoter/origin structure of the complementary sequence of IRES and found that the first and second stem-loops worked as negative and positive elements in RNA synthesis, respectively. The complementary strand of the second stem-loop of IRES was an important element also for binding to HCV RdRp.