Translation of poliovirus RNA: role of an essential cis-acting oligopyrimidine element within the 5' nontranslated region and involvement of a cellular 57-kilodalton protein.

Translation of poliovirus RNA is initiated by cap-independent internal entry of ribosomes into the 5' nontranslated region. This process is dependent on elements within the 5' nontranslated region (the internal ribosomal entry site) and may involve novel translation factors. Systematic mutation of a conserved oligopyrimidine tract has revealed a cis-acting element that is essential for translation in vitro. The function of this element is related to its position relative to other cis-acting domains. This element is part of a more complex structure that interacts with several cellular factors, but changes in protein binding after mutation of this element were not detected in a UV cross-linking assay. A 57-kDa protein from the ribosomal salt wash fraction of HeLa cells was identified that binds upstream of the oligopyrimidine tract. Translation of poliovirus mRNA in vitro was strongly and specifically inhibited by competition with the p57-binding domain (nucleotides 260 to 488) of the 5' nontranslated region of encephalomyocarditis virus, indicating a probable role for p57 in poliovirus translation. p57 is likely to be identical to the ribosome-associated factor that binds to and is necessary for the function of the internal ribosomal entry site of encephalomyocarditis virus RNA.