Mutations in the tryptophanyl-transfer ribonucleic acid ligase of E. coli causing temperature-sensitivity for growth.

Strains of Escherichia coli K-12 with altered tryptophanyl-tRNA ligases, conferring temperature-sensitivity for growth, have been isolated as spontaneous one-step mutants. The mutated enzymes differ markedly in activity from the wildtype, even at the permissive temperature. When assayed at the non-permissive temperature, the mutant enzymes are completely inactive. In one of the mutant strains, growth can be completely inhibited by addition of L-phenylalanine or L-tyrosine to the medium.