The article provides information on a study by P. Sarnow and colleagues on the interaction of a liver-specific miRNA (miR-122) with a target sequence on the 5' noncoding region (NCR) of the hepatitis C virus (HCV) RNA genome and promote viral replication. The region of the HCV RNA was inserted with miR-122 binding site into either the 5' or the 3' NCR of a luciferace reporter in liver cells to address the importance of the 5' position for the miR-122 binding site for stimulating replication.