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

Singh, Nongmaithem Sadananda and Varshney, Umesh (2004) A physiological connection between tmRNA and peptidyl-tRNA hydrolasefunctions in Escherichia coli. In: Nucleic Acids Research, 32 (20). pp. 6028-6037.

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Official URL: http://nar.oxfordjournals.org/content/32/20/6028


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 $(pth^t^s)$. Conversely, a null mutation in ssrA enhances the temperature-sensitive phenotype of the $pth^t^s$ 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 $pth^t^s$ strains. We discuss the physiological relevance of these observations to highlight a major role of tmRNA in decreasing cellular peptidyl-tRNA load.

Item Type: Journal Article
Additional Information: The copyright of this article belongs to Oxford University Press.
Department/Centre: Division of Biological Sciences > Microbiology & Cell Biology
Depositing User: Ravi V Nandhan
Date Deposited: 10 Jan 2005
Last Modified: 18 Jan 2012 08:44
URI: http://eprints.iisc.ac.in/id/eprint/2530

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