The effects of excision repair and the plasmid pKM101 on the induction of his+ revertants by chemical agents in Salmonella typhimurium.

Expansion of the Ames Salmonella/microsome mutagenesis test to include plasmid pKM101-bearing, excision repair-proficient derivatives permits 1) the identification of mutagens that require both factors for activity; 2) the identification of genotoxins through the enhancement of survival by excision repair; and 3) the classification of substances according to the effects of excision repair on their mutagenesis. Class I includes substances that require excision repair to effect mutagenesis. Class II contains substances whose mutagenesis is not affected by excision repair. Class III mutagens cause premutational lesions in DNA which are readily removed by excision repair. This classification scheme is suggested as a preliminary step in making a risk estimation for a mutagen.