Down-regulation of translation driven by hepatitis C virus internal ribosomal entry site by the 3 ' untranslated region of RNA

The genome of hepatitis C virus (HCV) is a single-stranded RNA of positive polarity that has a poly(U/C) tract followed by a highly conserved 98-nt se quence, termed the X region, in the 3' untranslated region (UTR). To invest igate the effect of the 3'UTR on the HCV translation that depends on the in ternal ribosomal entry site (IRES), we prepared a deletion HCV RNA, MA Delt a, that lacked the RNA region from nt 1286 to 8785. A series of MA Delta RN As that differ in the primary structure of their 3'UTR, were generated and examined for their translation efficiencies in reticulocyte lysates. Deleti on of the poly(U/C) tract and/or stem-loop structure (SL) 3 region of 3'X r esulted in enhancement of the translation efficiency. Translation of MA Del ta RNA was inhibited by the addition of recombinant polypyrimidine tract-bi nding protein (PTB). A similar inhibition by PTB, however, was observed whe n an RNA lacking the poly(U/C) tract or SL3 region was used. The inhibitory effect by PTB was not obvious for MA Delta (1041) RNA composed of nt 1 to 1041 but MA Delta (8928) RNA composed of nt 1 to 1285 and nt 8786 to 8928. These results suggest that the observed down-regulation of HCV translation by the 3'UTR is mediated by some host factor(s) other than PTB, and that a PTB site for inhibition resides in the coding sequence of nt 1042 to 8928 o f MA Delta RNA.