Abstract
As translation proceeds, the nascent polypeptide chain passes through a tunnel in the large ribosomal subunit. Although this ribosomal exit tunnel was once thought only to be a passive conduit for the growing nascent chain, accumulating evidence suggests that it may in fact play a more active role in regulating translation and initial protein folding events. Here we have determined single-particle cryo–electron microscopy reconstructions of eukaryotic 80S ribosomes containing nascent chains with high α-helical propensity located within the exit tunnel. The maps enable direct visualization of density for helices as well as allowing the sites of interaction with the tunnel wall components to be elucidated. In particular regions of the tunnel, the nascent chain adopts distinct conformations and establishes specific contacts with tunnel components, both ribosomal RNA and proteins, that have been previously implicated in nascent chain–ribosome interaction.
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Acknowledgements
We would like to thank B. Beatrix for help with the wheat germ translation system and J. Buerger for help with the electron microscopy. This research was supported by Federation of European Biochemical Societies and Knut och Alice Wallenbergs Stiftelse postdoctoral fellowships (to S.B.), grants from the Deutsche Forschungsgemeinschaft SFB594 and SFB646 (to R.B.), SFB740 (to T.M.) and WI3285/1-1 (to D.N.W.) and by the European Union and Senatsverwaltung für Wissenschaft, Forschung und Kultur Berlin.
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S.B., M.G. and R.B. designed research; S.B. prepared the complexes and collected data; O.B. and T.M. helped with data collection; S.B., M.G. and M.H. processed datasets; J.-P.A., A.J. and D.N.W. prepared models; S.B., D.N.W. and R.B. analyzed results, prepared figures and wrote the paper.
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Bhushan, S., Gartmann, M., Halic, M. et al. α-Helical nascent polypeptide chains visualized within distinct regions of the ribosomal exit tunnel. Nat Struct Mol Biol 17, 313–317 (2010). https://doi.org/10.1038/nsmb.1756
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DOI: https://doi.org/10.1038/nsmb.1756