Temperature-sensitive nonsense mutations in essential genes of Escherichia coli

Cells containing nonsense mutations in essential genes have been isolated in a strain of Escherichia coli that carried the su4(ts) gene which specifies a temperature-sensitive tyrosine transfer ribonucleic acid. Such cells are unable to form colonies at temperatures which inactivate this suppressor transfer ribonucleic acid. A screening procedure for the identification of mutants that carry temperature-sensitive nonsense mutations in essential genes is described, and certain properties of two such mutants are reported.