SOS-INDUCING ABILITY OF NATIVE AND MUTANT MICROBIAL RIBONUCLEASES

The results of genotoxicity testing of microbial ribonucleases from Ba cillus species with different catalytic activity obtained by site-dire cted mutagenesis in SOS chromotest are reported. At the concentrations 0.1-1 mg/ml, the induction factor for wild-type bacillar binase, barn ase and mutant Arg(58)Lys binase with 100% activity was found to be si gnificantly higher than 1.5 (1.8-2.8). Mutant RNases having decreased catalytic activity (binases with replacements Lys(26)Ala, Arg(61)Gln, His(101)Glu) or through natural inhibitor barstar inactivated wild-typ e RNase exhibited no SOS-inducing potency. The ability of native bacil lar RNases and mutant enzymes possessing high catalytic activity compa rable with the activity of wild-type RNase to cause the SOS response i ndicates that genotoxicity is mediated through the probable cleavage o f cellular RNA. The possible mechanisms of mutagenesis induced by cata lytically active RNases are discussed.