Protein Synthesis. Rqc2p and 60S Ribosomal Subunits Mediate mRNA-independent Elongation of Nascent Chains

Science. 2015 Jan 2;347(6217):75-8. doi: 10.1126/science.1259724.

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").

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cryoelectron Microscopy
  • Nucleic Acid Conformation
  • Peptide Biosynthesis, Nucleic Acid-Independent*
  • Protein Conformation
  • RNA, Messenger / metabolism
  • RNA, Transfer, Ala / chemistry
  • RNA, Transfer, Ala / metabolism
  • RNA, Transfer, Thr / chemistry
  • RNA, Transfer, Thr / metabolism
  • RNA-Binding Proteins
  • Ribosome Subunits, Large, Eukaryotic / chemistry
  • Ribosome Subunits, Large, Eukaryotic / metabolism*
  • Ribosome Subunits, Large, Eukaryotic / ultrastructure
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Saccharomyces cerevisiae Proteins / ultrastructure
  • Ubiquitin-Protein Ligases / metabolism*
  • Ubiquitin-Protein Ligases / ultrastructure

Substances

  • RNA, Messenger
  • RNA, Transfer, Ala
  • RNA, Transfer, Thr
  • RNA-Binding Proteins
  • Saccharomyces cerevisiae Proteins
  • Tae2 protein, S cerevisiae
  • Ltn1 protein, S cerevisiae
  • Rkr1 protein, S cerevisiae
  • Ubiquitin-Protein Ligases