Streptomycin-suppressible lethal mutations in Escherichia coli

Forty-one mutants have been isolated which require streptomycin for growth on complete medium. These streptomycin-suppressible lethal mutations are located randomly around the Escherichia coli genetic map; during growth in liquid culture, they exhibit a variety of responses to the removal of streptomycin as judged by turbidity, cell morphology, and macromolecular synthesis. In particular, some mutants are primarily affected in protein or ribonucleic acid (RNA) synthesis (or both), one in deoxyribonucleic acid synthesis, and two in lipid synthesis. Ten mutants affected in protein synthesis were examined for the activities of all twenty aminoacyl-transfer RNA synthetases, and three were found to have altered glutamyl-transfer RNA synthetase activities. The advantages of this method for isolating a wide variety of conditional lethal mutants are discussed.