Abstract
Internal ribosome entry sites (IRESs) facilitate an alternative, end-independent pathway of translation initiation. A particular family of dicistroviral IRESs can assemble elongation-competent 80S ribosomal complexes in the absence of canonical initiation factors and initiator transfer RNA. We present here a cryo-EM reconstruction of a dicistroviral IRES bound to the 80S ribosome. The resolution of the cryo-EM reconstruction, in the subnanometer range, allowed the molecular structure of the complete IRES in its active, ribosome-bound state to be solved. The structure, harboring three pseudoknot-containing domains, each with a specific functional role, shows how defined elements of the IRES emerge from a compactly folded core and interact with the key ribosomal components that form the A, P and E sites, where tRNAs normally bind. Our results exemplify the molecular strategy for recruitment of an IRES and reveal the dynamic features necessary for internal initiation.
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Acknowledgements
This work was supported by a grant from the VolkswagenStiftung (to C.M.T.S.), by US National Institutes of Health grant R01 GM60635 (to P.A.P.), by the sixth EU framework program 3DEM and by the European Union and Senatsverwaltung für Wissenschaft, Forschung und Kultur Berlin (UltraStructureNetwork and Anwenderzentrum). S.R.C. was supported with a grant from the Alexander von Humboldt Stiftung.
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Supplementary information
Supplementary Fig. 1
Resolution curve. (PDF 462 kb)
Supplementary Fig. 2
Comparison of the PKIII pseudoknot with the BWYV pseudoknot. (PDF 2493 kb)
Supplementary Fig. 3
Annotated secondary structure diagram. (PDF 1382 kb)
Supplementary Fig. 4
Comparison of the human telomerase pseudoknot with PKI of the CrPV IRES. (PDF 1981 kb)
Supplementary Fig. 5
Interactions of the CRPV IRES with the 80S ribosome. (PDF 2623 kb)
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Schüler, M., Connell, S., Lescoute, A. et al. Structure of the ribosome-bound cricket paralysis virus IRES RNA. Nat Struct Mol Biol 13, 1092–1096 (2006). https://doi.org/10.1038/nsmb1177
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DOI: https://doi.org/10.1038/nsmb1177
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