Minimal translation of the tmRNA tag-coding region is required for ribosome release.
The trans-translation system in bacteria promotes recycling of stalled ribosomes and targets incomplete peptides for proteolysis. In Escherichia coli, loss of trans-translation function has little effect on growth under normal laboratory conditions. Among the subtle phenotypes of tmRNA-deficient mutants is the inability to plate certain lambda imm(P22) phages. This phenotype is dependent on the ribosome recycling functions of the trans-translation system but is independent of its proteolysis-targeting activity. The experiments described here show that translation of the first (resume) codon of the tmRNA open reading frame by a tRNA is both necessary and sufficient for ribosome recycling. While a variety of sense codons can replace the naturally-occurring GCA alanine codon as the resume codon, both AAA and AAG lysine codons are non-functional resume codons. These results suggest that the main function of tmRNA in releasing stalled ribosomes is to supply a stop codon and so facilitate termination and subsequent ribosome recycling.
O'Connor
Michael
M
School of Biological Sciences, University of Missouri-Kansas City, Kansas City, MO 64110, USA. oconnormi@umkc.edu
D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics*; D020224:Expressed Sequence Tags; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics*; D010454:Peptide Termination Factors / Q000235:genetics; D014176:Protein Biosynthesis / Q000235:genetics*; D012329:RNA, Bacterial / Q000235:genetics*; D012270:Ribosomes / Q000235:genetics*
D010454:Peptide Termination Factors; D012329:RNA, Bacterial; C096222:tmRNA