Components of the multifactor complex needed for internal initiation by the IRES of hepatitis C virus in Saccharomyces cerevisiae

Interaction between the 40S ribosomal subunit and the IRES of hepatitis C virus (HCV) is thought to be independent of initiation proteins, while joining of the 60S ribosomal subunit, and initiation of translation is dependent upon components of the translation machinery. An established in vivo functional assay for internal initiation mediated by the HC V IRES was used to identify proteins needed for IRES dependent translation in Saccharomyces cerevisiae strains possessing alterations of the translation machinery. Internal initiation dependent upon the HC V IRES was abrogated in strains lacking eIF5B, and reduced in strains with altered eIF3, either lacking the Hcr1p subunit, a component of eIF3 not previously known to interact with HC V RNA, or possessing an amino acid change in the Rpg1p subunit. The HC V RNAinduced conformational change in the 40S subunit might affect positioning of eIF3 and lead to different interactions between the ribosome, eIF3, and the multifactor complex. HC V IRES dependent initiation was unaffected in strains in which the concentration of the initiating tRNA was reduced. Alteration of the d subunit of eIF2B, which leads to inefficient recycling or substitution of aspartic acid for serine 51 of eIF2a had no effect on internal initiation. Production of human Pkr inhibited HC V IRES dependent initiation in yeast. The synthesis of Pkr in yeast is known to result in high levels of eIF2a phosphorylation, increased Gcn4p synthesis, and reduced ribosomal protein production. These alterations may explain the effect of Pkr synthesis on HC V IRES dependent initiation in yeast.