Induction of the SOS response by ICR191 does not influence frameshift mutagenesis at the hisC3076 marker of Salmonella typhimurium.

Reversion of the Salmonella typhimurium frameshift marker hisC3076 by ICR191 and 9-aminoacridine in rec+ and recA1 backgrounds was examined using the standard plate-reversion assay. For both compounds, the level of reversion observed in the recA strain is significantly greater than in the rec+ strain. Thus reversion of hisC3076 is not recA-dependent, but is recA-modulated. The ability of a mutagen (or mutagenic treatment) to induce the recA lexA-dependent SOS response does not therefore imply that mutagenic effects will also be recA-dependent.