TRANSLATION OF HUMAN HEPATITIS-C VIRUS-RNA IN CULTURED-CELLS IS MEDIATED BY AN INTERNAL RIBOSOME-BINDING MECHANISM

The human hepatitis C virus (HCV) contains a long 5' noncoding region (5' NCR). Computer-assisted and biochemical analyses suggest that ther e is a complex secondary structure in this region that is comparable t o the secondary structures that are found in picornaviruses (E. A. Bro wn, H. Zhang, L.-H. Ping, and S. M. Lemon, Nucleic Acids Res. 20:5041- 5045, 1992). Previous in vitro studies suggest that the HCV 5' NCR pla ys an important role during translation (K. Tsukiyama-Kohara, N. Iizuk a, M. Kohara, and A. Nomoto, J. Virol. 66:1476-1483, 1992). Dicistroni c and monocistronic expression vectors, in vitro translation, RNA tran sfections, and deletion mutagenesis studies were utilized to demonstra te unambiguously that the HCV 5' NCR is involved in translational cont rol. Our data strongly support the conclusion that an internal ribosom e entry site exists within the 5' noncoding sequences proximal to the initiator AUG. Furthermore, our results suggest that the HCV genome is translated in a cap-independent manner and that the sequences immedia tely upstream of the initiator AUG are essential for internal ribosome entry site function during translation.