SOS independent survival against mitomycin C induced lethality in a rifampicin-nalidixic acid-resistant mutant of Escherichia coli

A combination of specific rifampicin-resistant (rpo B87) and nalidixic acid-resistant (gyrA87) mutations results in a marked increase in the survival of Escherichia coli against mitomycin C-induced lethality in mutants defective for SOS induction and excision repair. Although the response does not seem to be obligatorily dependent upon the RecA protein, the efficiency is markedly increased in its presence, even in a conventionally inactive form. This response is not elicited against lethality due to ultraviolet radiation or N-methyl-N′-nitro-N-nitrosoguanidine exposure. The combination of rpo B87 and gyrA87 mutations also greatly alleviates post-mitomycin C degradation of DNA under SOS non-inducible conditions. It is proposed that the rpo B subunit of RNA polymerase and gyrA subunit of DNA gyrase could participate in the repair of certain types of DNA damage, such as cross-links, in a mode independent of SOS-regulated excision repair and post-replication repair.