Initiation of Translation by Cricket Paralysis Virus IRES Requires Its Translocation in the Ribosome

• Published in: Cell Vol. 157; no. 4; pp. 823 - 831
• Main Authors: Fernández, Israel S., Bai, Xiao-Chen, Murshudov, Garib, Scheres, Sjors H.W., Ramakrishnan, V.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 08-05-2014; Cell Press
• Subjects: Cricket paralysis virus; Cryoelectron Microscopy; Dicistroviridae - chemistry; Dicistroviridae - genetics; Kluyveromyces - chemistry; Kluyveromyces - metabolism; Kluyveromyces lactis; Models, Molecular; Peptide Chain Initiation, Translational; Ribosomes - chemistry; Ribosomes - metabolism; Ribosomes - ultrastructure; RNA, Messenger - chemistry; RNA, Messenger - genetics; RNA, Messenger - metabolism; RNA, Messenger - ultrastructure; RNA, Transfer - metabolism; RNA, Viral - chemistry; RNA, Viral - genetics; RNA, Viral - metabolism; RNA, Viral - ultrastructure
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/j.cell.2014.04.015

The cricket paralysis virus internal ribosome entry site (CrPV-IRES) is a folded structure in a viral mRNA that allows initiation of translation in the absence of any host initiation factors. By using recent advances in single-particle electron cryomicroscopy, we have solved the structure of CrPV-IRES bound to the ribosome of the yeast Kluyveromyces lactis in both the canonical and rotated states at overall resolutions of 3.7 and 3.8 Å, respectively. In both states, the pseudoknot PKI of the CrPV-IRES mimics a tRNA/mRNA interaction in the decoding center of the A site of the 40S ribosomal subunit. The structure and accompanying factor-binding data show that CrPV-IRES binding mimics a pretranslocation rather than initiation state of the ribosome. Translocation of the IRES by elongation factor 2 (eEF2) is required to bring the first codon of the mRNA into the A site and to allow the start of translation.
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•The high-resolution structure of CrPV-IRES bound to the ribosome was solved by cryoEM•Pseudoknot I of CrPV-IRES binds in the decoding center, thus blocking the A site•CrPV-IRES mimics a pretranslocation rather than initiation complex of the ribosome•Translocation of CrPV-IRES by eEF2 is required for the start of translation
A high-resolution structure of the cricket paralysis virus IRES bound to the eukaryotic ribosome reveals a surprising mechanism of translation initiation that requires a translocation step.