title: Translational termination without a stop codon.
abstract: Ribosomes stall when they encounter the end of messenger RNA (mRNA) without an in-frame stop codon. In bacteria, these "nonstop" complexes can be rescued by alternative ribosome-rescue factor A (ArfA). We used electron cryomicroscopy to determine structures of ArfA bound to the ribosome with 3'-truncated mRNA, at resolutions ranging from 3.0 to 3.4 angstroms. ArfA binds within the ribosomal mRNA channel and substitutes for the absent stop codon in the A site by specifically recruiting release factor 2 (RF2), initially in a compact preaccommodated state. A similar conformation of RF2 may occur on stop codons, suggesting a general mechanism for release-factor-mediated translational termination in which a conformational switch leads to peptide release only when the appropriate signal is present in the A site.
authors.affiliation: Medical Research Council (MRC) Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
authors.forename: Nathan R
authors.initials: NR
authors.lastname: James
authors.affiliation: Medical Research Council (MRC) Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
authors.forename: Alan
authors.initials: A
authors.lastname: Brown
authors.affiliation: Medical Research Council (MRC) Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
authors.forename: Yuliya
authors.initials: Y
authors.lastname: Gordiyenko
authors.affiliation: Medical Research Council (MRC) Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK. ramak@mrc-lmb.cam.ac.uk.
authors.forename: V
authors.initials: V
authors.lastname: Ramakrishnan
mesh_terms: D020413:3' Untranslated Regions; D018388:Codon, Terminator; D020285:Cryoelectron Microscopy; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D010443:Peptide Chain Termination, Translational; D010454:Peptide Termination Factors / Q000737:chemistry* / Q000378:metabolism; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D055550:Protein Stability; D012329:RNA, Bacterial / Q000737:chemistry; D012335:RNA, Ribosomal / Q000737:chemistry / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D020413:3' Untranslated Regions; C556014:ArfA protein, E coli; D018388:Codon, Terminator; D029968:Escherichia coli Proteins; D010454:Peptide Termination Factors; D010455:Peptides; D012329:RNA, Bacterial; D012335:RNA, Ribosomal; D016601:RNA-Binding Proteins; C041460:peptide chain termination release factor 2