Derepressed levels of the isoleucine-valine and leucine enzymes in his T 1504, a strain of Salmonella typhimurium with altered leucine transfer ribonucleic acid.

A hisT mutant of Salmonella typhimurium was found to have altered regulation of the isoleucine-valine and leucine enzymes. These enzymes in the hisT strain were derepressed two- to eightfold over those of the parent wild-type strain when grown in minimal medium or under repressing conditions. The amount of tRNA(Leu) and the cellular concentration of charged tRNA(Leu) was about the same in the hisT strain and in the wild type. However, leucyl-tRNA from the mutant was chromatographically different from that of wild type, confirming previous reports that hisT strains have altered tRNA(Leu). These results suggest strongly that tRNA(Leu) is involved in repression of the isoleucine-valine and leucine enzymes in S. typhimurium.