Alteration of the Intracellular Concentration of Aminoacyl‐tRNA Synthetases and Isoaccepting tRNAs during Amino‐Acid‐Limited Growth in Escherichia coli

Growth of Escherichia coli AB 2271 under threonine or isoleucine deficiency leads to a derepression of the threonyl‐tRNA synthetase and isoleucyl‐tRNA synthetase respectively. During this amino‐acid‐limited growth the concentrations of isoaccepting fractions of the cognate tRNA species were changed, as demonstrated by their altered reversed‐phase‐5 chromatograms. But, in addition, the profiles of the isoacceptors of all other tRNA species investigated, i.e. of tRNAs Leu , tRNAs Ser and tRNAs Arg were also altered. This means that, if there is a correlation between regulation of the level of an aminoacyl‐tRNA synthetase and its cognate isoaccepting tRNAs, it is superimposed by the effect of amino acid limitation upon the concentration of all isoaccepting tRNAs. So far drastic changes in profiles of isoaccepting tRNAs have only been observed under unbalanced growth in relaxed cells or during treatment with antibotis. Here we demonstrate that similar heavy alterations in patterns of isoaccepting tRNAs occur in a proven stringent E. coli strain growing exponentially under amino acid limitation signal a meaningful biological function of those newly or increasingly occuring isoaccepting tRNAs. During the growth under amino acid limitation the total acceptor activity of eight investigated tRNA species, however, stayed unchanged, except that under threonine‐limited growth the total amount of tRNA Ile was reduced to about half and that of tRNA Glu increased; both tRNA species of these isoacceptors are known [30,31] as spacers between ribosomal RNAs.