INDUCTION OF 3-METHYLADENINE DNA GLYCOSYLASE-II IS RECA+-INDEPENDENT

The recA1 mutation was transduced into the tag-2 mutant of Escherichia coli, thus making a strain deficient in the induction of SOS repair as well as in the constitutive repair of 3-alkylated adenines in DNA. The double mutant recA tag is more sensitive to methyl methanesulfonate exposure than either single mutant, indicating that recA and tag mutations block different pathways in repair of alkylation damage. The double mutant is more deficient in host cell reactivation of alkylated phages than the tag single mutant. However, alkylation induction of the double mutant with N-methyl-N''-nitro-N-nitrosoguanindine resulted in killing adaptation of the cells to methyl methanesulfonate and restored the host cell reactivation capacity for alkylated .lambda. phage to wild-type levels. These adaptive responses can be ascribed to the induction of 3-methyladenine DNA glycosylase II which is shown by enzyme analysis to proceed normally in the recA mutant background. The results imply that the induction of the alkA gene encoding 3-methyladenine DNA glycosylase II is independent of SOS induction.