Unlabelled: miR-122 is a liver-specific microRNA (miRNA) that binds to two sites (S1 and S2) on the 5' untranslated region (UTR) of the hepatitis C virus (HCV) genome and promotes the viral life cycle. It positively affects viral RNA stability, translation, and replication, but the mechanism is not well understood. To unravel the roles of miR-122 binding at each site alone or in combination, we employed miR-122 binding site mutant viral RNAs, Hep3B cells (which lack detectable miR-122), and complementation with wild-type miR-122, an miR-122 with the matching mutation, or both.