Interaction of hepatitis C virus core protein with viral sense RNA and suppression of its translation

To clarify the binding properties of hepatitis C virus (HCV) core protein a nd its viral RNA for the encapsidation, morphogenesis, and replication of H CV, the specific interaction of HCV core protein with its genomic RNA synth esized in vitro was examined in an in vivo system. The positive-sense RNA f rom the 5' end to nucleotide (nt) 2327, which covers the 5' untranslated re gion (5'UTR) and a part of the coding region of HCV structural proteins, in teracted with HCV core protein, while no interaction was observed in the sa me region of negative-sense RNA and in other regions of viral and antiviral sense RNAs. The internal ribosome entry site (IRES) exists around the 5'UT R of HCV; therefore, the interaction of the core protein with this region o f HCV RNA suggests that there is some effect on its cap-independent transla tion. Cells expressing HCV core protein were transfected with reporter RNAs consisting of nt I to 709 of HCV RNA (the 5'UTR of HCV and about two-third s of the core protein coding regions) followed by a firefly luciferase gene (HCV07Luc RNA). The translation of HCV07Luc RNA was suppressed in cells ex pressing the core protein, whereas no significant suppression was observed in the case of a reporter RNA possessing the IRES of encephalomyocarditis v irus followed by a firefly luciferase. This suppression by the core protein occurred in a dose-dependent manner. The expression of the E1 envelope pro tein of HCV or beta-galactosidase did not suppress the translation of both HCV and EMCV reporter RNAs. We then examined the regions that are important for suppression of translation by the core protein and found that the regi on from nt 1 to 344 was enough to exert this suppression. These results sug gest that the HCV core protein interacts with viral genomic RNA at a specif ic region to form nucleocapsids and regulates the expression of HCV by inte racting with the 5'UTR.