Peptidyl transfer RNA dissociates during protein synthesis from ribosomes of Escherichia coli

Natural premature protein synthesis termination can be reduced in Escherichia coli by decreased translation rates

Peptidyl tRNA hydrolase is an essential enzyme for normal growth inasmuch as a mutant strain of Escherichia coli with a temperature-sensitive hydrolase cannot continue protein synthesis at the non-permissive temperature. In the absence of hydrolase peptidyl tRNA rapidly accumulates. Why peptidyl tRNA should be formed is the subject of this report. The rapid rate of protein synthesis is likely one mechanism of formation of peptidyl tRNA. A strA mutant of the hydrolase (pth-1) mutant strain that has a 40% reduction in amino acid polymerization rate can grow at 42 degrees C. StrA mutants with normal polymerization rates, however, cannot grow at 42 degrees C when pth-1 is present. Furthermore, addition of low levels of chloramphenicol (2--4 micrograms/ml) but not several other tested drugs, phenotypically suppressed pth-1 at 42 degrees C. Chloramphenicol, at these concentrations, was found to reduce the amino acid polymerization rate 30--40%. On the other hand, no evidence could be found that amino acyl tRNA selection errors are incorporated into pseudo revertants of the pth-1 strain.

Accumulation of peptidyl tRNA is lethal to Escherichia coli

A mutant strain of Escherichia coli with temperature-sensitive peptidyl-tRNA hydrolase grows at 30 degrees C but, when shifted to 40 degrees C, dies at rates affected by physiological, pharmacological, and genetical perturbations. The rate of killing correlates with the relative accumulation of peptidyl-tRNA, suggesting that it is responsible for the death of the cells.

Ribosome editing and the error catastrophe hypothesis of cellular aging

Ribosome editing involves the dissociation during protein synthesis of inappropriate peptidyl-tRNA's, ones whose structure does not correctly complement the codon of the mRNA. This process is one of three stages in protein biosynthesis in which the frequency of errors in cellular proteins is controlled. These stages are reviewed and the implications of ribosome editing are described. A model for stability of the translation apparatus is criticized. Calculations using a revision of the model and experimentally reasonable values for the various parameters show varying time courses for error catastrophes.