Hepatitis C Virus 5'UTR Sequences That Bind eIF3 and Ribosomal 40S Subunits Confer Stimulation of Minus-Strand RNA Synthesis.

Hepatitis C Virus (HCV) is a plus-strand RNA virus that replicates its genome via a minus-strand intermediate, which in turn is the template for the synthesis of progeny plus-strand genomes. In order to characterize sequence elements in the HCV 5'-untranslated region (5'UTR) that are possibly involved in the regulation of minus-strand RNA synthesis starting at the genome's 3'end, we used a replicon system in which a possible function of these sequences is uncoupled from other functions like translation regulation. For the specific detection by RT-qPCR of minus strands newly synthesized in the cells from the transfected replicon RNAs, we carefully eliminated the contaminating DNA and transfected RNA and avoided self-priming caused by hairpin formation. We found that the absence of any HCV sequences at the 5'end does not allow genome replication. Stem-loop I-II sequences only allow extremely low-level replication, whereas the presence of stem-loops I-III or the complete 5'UTR allows efficient replication. The mutation of sequences required for the binding of translation initiation factor 3 (eIF3) and the ribosomal 40S subunit in the 5'UTR of the plus strand severely impairs minus-strand synthesis. This suggests that eIF3 and the 40S subunit are involved in plus-strand 5'-3'-end communication and the regulation of minus-strand synthesis.