Translational Enhancement by the 3'-untranslated Region of Hepatitis C Virus RNA

Hepatitis C virus (HCV) RNA has an internal ribosome entry site (IRES) in the 5'-untranslated region (UTR) and an X region in the 3'-UTR. The IRES and the X-region regulate HCV translation. HCV translation is enhanced by the X region through interaction with the polypyrimidine-tractbinding protein (PTB) . Recently, several cellular factors that bind both ends of HCV RNA were identified. However, the function of these binding factors remains unclear. HCV RNA also contains a long poly (U/C) region just upstream of the X region. The function of this poly (U/C) region on HCV translation is also uncertain. In this study, we analyzed the role of the entire 3'-UTR on HCV translation using various translation systems. We constructed T7-based plasmids containing the 5'-UTR, the luciferase (LUC) gene as a reporter, and the entire 3'-UTR containing the variable region, poly (U/C) stretch, and the X region (HCV 5'L3') . We also prepared plasmids in which the core (HCV 5'CL3') or the core-to-E2 (HCV 5'CE1E2L3') region was inserted preceding the LUC gene. In vitro translation of HCV 5'CE1E2L3' using rabbit reticulocyte lysates (RRL) showed a 25-fold enhancement by the entire 3'-UTR. We also demonstrated this translational enhancement by the 3'-UTR in animal cell culture systems using Huh7, HeLa, and HepG2 cells. In conclusion, the entire 3'-UTR can enhance translation of HCV RNA in both rabbit reticulocyte lysates and in animal cell culture systems.