A physiological connection between tmRNA and peptidyl-tRNA hydrolase functions in Escherichia coli

Nucleic Acids Res. 2004 Nov 16;32(20):6028-37. doi: 10.1093/nar/gkh924. Print 2004.

Abstract

The bacterial ssrA gene codes for a dual function RNA, tmRNA, which possesses tRNA-like and mRNA-like regions. The tmRNA appends an oligopeptide tag to the polypeptide on the P-site tRNA by a trans-translation process that rescues ribosomes stalled on the mRNAs and targets the aberrant protein for degradation. In cells, processing of the stalled ribosomes is also pioneered by drop-off of peptidyl-tRNAs. The ester bond linking the peptide to tRNA is hydrolyzed by peptidyl-tRNA hydrolase (Pth), an essential enzyme, which releases the tRNA and the aberrant peptide. As the trans-translation mechanism utilizes the peptidyl-transferase activity of the stalled ribosomes to free the tRNA (as opposed to peptidyl-tRNA drop-off), the need for Pth to recycle such tRNAs is bypassed. Thus, we hypothesized that tmRNA may rescue a defect in Pth. Here, we show that overexpression of tmRNA rescues the temperature-sensitive phenotype of Escherichia coli (pth(ts)). Conversely, a null mutation in ssrA enhances the temperature-sensitive phenotype of the pth(ts) strain. Consistent with our hypothesis, overexpression of tmRNA results in decreased accumulation of peptidyl-tRNA in E.coli. Furthermore, overproduction of tmRNA in E.coli strains deficient in ribosome recycling factor and/or lacking the release factor 3 enhances the rescue of pth(ts) strains. We discuss the physiological relevance of these observations to highlight a major role of tmRNA in decreasing cellular peptidyl-tRNA load.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles
  • Carboxylic Ester Hydrolases / genetics
  • Carboxylic Ester Hydrolases / metabolism
  • Carboxylic Ester Hydrolases / physiology*
  • Escherichia coli / enzymology
  • Escherichia coli / genetics*
  • Escherichia coli / metabolism
  • Escherichia coli Proteins / genetics
  • Mutation
  • Peptide Termination Factors / genetics
  • Phenotype
  • Promoter Regions, Genetic
  • RNA, Bacterial / genetics
  • RNA, Bacterial / metabolism
  • RNA, Bacterial / physiology*
  • RNA, Transfer, Amino Acyl / metabolism
  • Temperature

Substances

  • Escherichia coli Proteins
  • Peptide Termination Factors
  • RNA, Bacterial
  • RNA, Transfer, Amino Acyl
  • frr protein, E coli
  • peptide-chain-release factor 3
  • tRNA, peptidyl-
  • tmRNA
  • Carboxylic Ester Hydrolases
  • aminoacyl-tRNA hydrolase