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Enhancement of eukaryotic messenger RNA (mRNA) translation initiation by the 3' poly(A) tail is mediated through interaction of poly(A)-binding protein with eukaryotic initiation factor (eIF) 4G, bridging the 5' terminal cap structure. In contrast to cellular mRNA, translation of the uncapped, non-polyadenylated hepatitis C virus (HCV) genome occurs independently of eIF4G and a role for 3'-untranslated sequences in modifying HCV gene expression is controversial. Utilizing cell-based and in vitro translation assays, we show that the HCV 3'-untranslated region (UTR) or a 3' poly(A) tract of sufficient length interchangeably stimulate translation dependent upon the HCV internal ribosomal entry site (IRES). However, in contrast to cap-dependent translation, the rate of initiation at the HCV IRES was unaffected by 3'-untranslated sequences. Analysis of post-initiation events revealed that the 3' poly(A) tract and HCV 3'-UTR improve translation efficiency by enabling termination and possibly ribosome recycling for successive rounds of translation.
Shelton S. Bradrick (Mon,) studied this question.