Three noncontiguous p57-binding sites were located within the poliovirus 5' nontranslated region, and binding was not solely dependent on a polyuridine tract.
The study identifies specific binding sites for the p57 polypeptide (PTB) within the poliovirus 5' nontranslated region, contributing to the understanding of viral translation initiation.
Initiation of translation of poliovirus RNA by ribosomal entry into an internal segment of the 742-nucleotide (nt)-long 5' nontranslated region involves trans-acting factors, including p57, a 57-kDa polypeptide which has been identified as the pyrimidine tract-binding protein (PTB). A UV cross-linking assay was used to compare the RNA-binding properties of the p57 present in various mammalian cytoplasmic extracts with those of purified murine p57 and recombinant human PTB. Three noncontiguous p57-binding sites were located within the poliovirus 5' nontranslated region, between nt 70 and 288, and 443 and 539 (domain V), and 630 and 730. With the same assay, a novel 34-kDa polypeptide was identified that bound nt 1 to 629 specifically. A single A-->G substitution of nt 480 which attenuates poliovirus did not alter UV cross-linking of p57 to domain V. Although UV cross-linking of p57 to the internal ribosome entry site was specifically reduced by competition with poly(U) but not by competition with poly(C), poly(G), and poly(A) homoribopolymers, the presence of a polyuridine tract was not a sufficient determinant for binding of RNA to the p57 present in cytoplasmic extracts, nor was the polypyrimidine tract downstream of domain V necessary for binding to this site.
Hellen et al. (Tue,) reported a other. p57 (pyrimidine tract-binding protein) was evaluated on RNA-binding properties and binding site locations. Three noncontiguous p57-binding sites were located within the poliovirus 5' nontranslated region, and binding was not solely dependent on a polyuridine tract.