Effect of the overproduction of phenylalanyl- and threonyl-tRNA synthetases on tRNAPhe and tRNAThr concentrations in E. coli cells.

Transformation of an E. coli strain with a recombinant plasmid DNA (pB1) encoding the genes for phenylalanyl- and threonyl-tRNA synthetases causes overproduction of these enzymes by about 100- and 5-fold, respectively. A possible effect of the overproduction of the two aminoacyl-tRNA synthetases on intracellular cognate tRNA levels has been searched for by comparing tRNAThr and tRNAPhe aminoacylation capacities in the RNA extracts from strains carrying pB1 or pBR322 plasmid DNA. The answer is that the levels of these tRNAs are not changed by selective increase of the cognate synthetases.