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Suppression of thermosensitive peptidyl-tRNA hydrolase mutation in Escherichia coli by gene duplication

UPR9073 du CNRS, Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, F-75005 Paris, France¹
Aventis Pharma SA, 13 Quai Jules Guesde, 94403 Vitry sur Seine Cedex, France²

Author for correspondence: Richard H. Buckingham. Tel: +33 1 5841 5120. Fax: +33 1 5841 5020. e-mail: rhb{at}ibpc.fr

Peptidyl-tRNA hydrolase (Pth) in Escherichia coli is required to recycle tRNA molecules that dissociate from the ribosome as peptidyl-tRNA during protein synthesis. At non-permissive temperatures, strains with a thermosensitive mutation affecting the enzyme accumulate peptidyl-tRNA, cease protein synthesis and die. The rate of reversion of this mutation to thermoresistance varies widely according to the genetic background of the cell and the temperature of selection; under certain conditions, reversion can occur at rates approaching 10^-3 per cell per generation. In such revertants, a chromosomal pth gene can be replaced by an inactivated gene, restoring thermosensitive growth in most cases. PCR amplification experiments and Southern blots show the presence of both normal and inactivated copies of the gene, demonstrating that gene duplication has occurred in the revertants. Estimation of intracellular peptidyl-tRNA hydrolase by Western blotting confirms this explanation of the mechanism of high-frequency reversion to thermoresistance.

Keywords: translation, ribosome, termination

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