An antibiotic dependent conditional lethal mutant with a lesion affecting transcription and translation.

A conditioned lethal mutant of E. coli was isolated which required the presence of either the RNA polymerase targeted antibiotic, rifampicin, or the ribosomally targeted antibiotic, kasugamycin, for survival. This mutant was characterised. The locus of the mutation responsible for the antibiotic dependent phenotype, ridA, was mapped at about 70.5 min on the chromosomal linkage map, between argR and fabE. The mutant was investigated as a candidate for a strain with a lesion in some cellular component acting on both RNA polymerase and the ribosome. A close interaction with RNA polymerase was evident from the interplay arising from the combination of ridA and various rpoB mutations as manifested in the phenotype. The ability of kasugamycin, but not other ribosomally targeted aminoglycoside antibiotics, to relieve the lethality due to the ridA mutation was an indication of the specificity in the interaction of the ridA gene product with the ribosome.