Mutant frequencies induced by methylating agents: (A) MMS, (B) MNNG and (C) MNU. In the small-sized graphs described at right side of each figure from (A) to (C), the mutant frequencies are shown with a small scale. Strains are NR10832 (wild-type), open circle; KT01121 (ada ogt), open triangle; NR12896 (mutS), closed circle; NR11102 (mutL), open square; NR12897 (mutH), closed square; and NR12999 (uvrA), closed triangle. Mutant frequencies are corrected by subtracting spontaneous mutant frequencies. Statistical analysis was performed using the Student’s t test. **P > 0.01 and *P > 0.05 compared with the mutant frequency for the wild-type.