Enzymatic Hydrolysis of N-Acyl-Aminoacyl Transfer RNAs

In a rapidly growing culture of E. coli, each cell contains approximately 30,000 ribosomes. For each ribosome, there are about 10 tRNA molecules out of the 40 or more existing species. Thus it is likely that during intense protein synthesis, at least certain tRNA molecules constitute a limiting factor in the rate of polypeptide chain growth. Any mechanism that renders aminoacyl-tRNA molecules unavailable for translation may be detrimental for the cell, since it would further decrease the number of functional tRNA molecules. Such would be the case, for instance, if growing peptide chains were accidentally released with their tRNAs from the protein-synthesizing machinery. In the cell, tRNA would not be recovered from peptidyl-tRNA, because the ester bond which unites the two parts of the molecule is very stable and its spontaneous hydrolysis is improbable. Furthermore, aminoacyl-tRNA synthetases are certainly unable to regenerate tRNAs from peptidyl-tRNAs, even if AMP and pyrophosphate...