The study demonstrates that IRES-mediated translation initiation requires the same canonical eukaryotic initiation factors (eIF2, eIF3, eIF4F) as cap-dependent initiation, but utilizes a novel cap-independent interaction with eIF4F.
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Preclinical findings only; extends mechanistic insight into IRES initiation but leaves open therapeutic relevance in vivo.
Translation of picornavirus RNA is initiated after ribosomal binding to an internal ribosomal entry site (IRES) within the 5' untranslated region. We have reconstituted IRES-mediated initiation on encephalomyocarditis virus RNA from purified components and used primer extension analysis to confirm the fidelity of 48S preinitiation complex formation. Eukaryotic initiation factor 2 (eIF2), eIF3, and eIF4F were required for initiation; eIF4B and to a lesser extent the pyrimidine tract-binding protein stimulated this process. We show that eIF4F binds to the IRES in a novel cap-independent manner and suggest that cap- and IRES-dependent initiation mechanisms utilize different modes of interaction with this factor to promote ribosomal attachment to mRNA.
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Pestova et al. (1996) studied this question.
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