TABLE 2.

Spontaneous mutation frequencies of mutSL- and mutY-deficient strains^a

Strain	Mean Rifr mutation frequency ± SD (10−9)b	Relative frequency
YB955	1.6 ± 0.92	1
mutYmutant	13.74 ± 0.217	8.58
mutY::amyE-Phs-mutY mutant	129.145 ± 18.52	80.71
mutSL mutant	106.67 ± 2.003	66.66
mutY mutSL mutant	74.53 ± 1.94	46.58

^aCells were grown for 12 h at 37°C in antibiotic A3 medium (Difco) supplemented with the proper antibiotics, and aliquots were plated on six LB plates containing 10 μg/ml rifampin. Rif^r colonies were counted after 1 day of incubation at 37°C.

^bValues shown are averages for three independent experiments ± standard deviations.