title: Escherichia coli YaeJ protein mediates a novel ribosome-rescue pathway distinct from SsrA- and ArfA-mediated pathways.
abstract: Accumulation of stalled ribosomes at the 3' end of mRNA without a stop codon (non-stop mRNA) is supposed to be toxic to bacterial cells. Escherichia coli has at least two distinct systems to rescue such stalled ribosomes: SsrA-dependent trans-translation and ArfA-dependent ribosome rescue. Combination of the ssrA and arfA mutations is synthetically lethal, suggesting the significance of ribosome rescue. In this study, we identified the E. coli yaeJ gene, encoding a peptide-release factor homologue with GGQ motif, as a multicopy suppressor of the lethal phenotype of ssrA arfA double mutant. The YaeJ protein was shown to bind to ribosomes. Both in vivo and in vitro, YaeJ showed the ribosome-rescue activity and promoted the hydrolysis of peptidyl-tRNA residing in the stalled ribosome. Missense mutation in the GGQ motif or deletion of the C-terminal unstructured tail abolished both the suppressor activity for ssrA arfA synthetic lethality and the ribosome-rescue activity, suggesting the importance of these structural features. On the basis of these observations, we propose that YaeJ acts as a stop codon-independent peptidyl-tRNA hydrolysing factor through binding to ribosomes stalled at the 3' end of non-stop mRNAs. It was also suggested that ArfA and YaeJ rescue the stalled ribosomes by distinct mechanisms.
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan.
authors.forename: Yuhei
authors.initials: Y
authors.lastname: Chadani
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Ono
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Kutsukake
authors.forename: Tatsuhiko
authors.initials: T
authors.lastname: Abo
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D002265:Carboxylic Ester Hydrolases / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D018628:Gene Dosage; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D011485:Protein Binding; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*; D016415:Sequence Alignment; D017384:Sequence Deletion
chemical_list: C556014:ArfA protein, E coli; D029968:Escherichia coli Proteins; D050505:Mutant Proteins; D012346:RNA, Transfer, Amino Acyl; D016601:RNA-Binding Proteins; C430328:small protein B; C019037:tRNA, peptidyl-; D002265:Carboxylic Ester Hydrolases; C558457:YaeJ protein, E coli; C019674:aminoacyl-tRNA hydrolase