Abstract
In Eukarya, stalled translation induces 40S dissociation and recruitment of the ribosome quality control complex (RQC) to the 60S subunit, which mediates nascent chain degradation. Here we report cryo-electron microscopy structures revealing that the RQC components Rqc2p (YPL009C/Tae2) and Ltn1p (YMR247C/Rkr1) bind to the 60S subunit at sites exposed after 40S dissociation, placing the Ltn1p RING (Really Interesting New Gene) domain near the exit channel and Rqc2p over the P-site transfer RNA (tRNA). We further demonstrate that Rqc2p recruits alanine- and threonine-charged tRNA to the A site and directs the elongation of nascent chains independently of mRNA or 40S subunits. Our work uncovers an unexpected mechanism of protein synthesis, in which a protein--not an mRNA--determines tRNA recruitment and the tagging of nascent chains with carboxy-terminal Ala and Thr extensions ("CAT tails").
Copyright © 2015, American Association for the Advancement of Science.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Cryoelectron Microscopy
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Nucleic Acid Conformation
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Peptide Biosynthesis, Nucleic Acid-Independent*
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Protein Conformation
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RNA, Messenger / metabolism
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RNA, Transfer, Ala / chemistry
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RNA, Transfer, Ala / metabolism
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RNA, Transfer, Thr / chemistry
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RNA, Transfer, Thr / metabolism
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RNA-Binding Proteins
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Ribosome Subunits, Large, Eukaryotic / chemistry
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Ribosome Subunits, Large, Eukaryotic / metabolism*
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Ribosome Subunits, Large, Eukaryotic / ultrastructure
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Saccharomyces cerevisiae / genetics
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Saccharomyces cerevisiae / metabolism*
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Saccharomyces cerevisiae Proteins / metabolism*
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Saccharomyces cerevisiae Proteins / ultrastructure
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Ubiquitin-Protein Ligases / metabolism*
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Ubiquitin-Protein Ligases / ultrastructure
Substances
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RNA, Messenger
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RNA, Transfer, Ala
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RNA, Transfer, Thr
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RNA-Binding Proteins
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Saccharomyces cerevisiae Proteins
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Tae2 protein, S cerevisiae
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Ltn1 protein, S cerevisiae
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Rkr1 protein, S cerevisiae
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Ubiquitin-Protein Ligases