TABLE 6.

Spontaneous mutation rates for dnaE alleles

Strain	Mutation rate (106)
	Base substitutions		Frameshifts
	mutS+	mutS	mutS+	mutS
BS40	0.011	0.68	0.048	34.4
BS40dnaE1336	0.25	7.6	0.34	61.0
BS40dnaE1337	0.077	5.2	0.20	81.1
BS40dnaE1338	6.0	8.8	20	137
BS40dnaE173	3.2	0.44	120	217

^aCultures were incubated overnight at 37°C in 1.5 ml of LB medium and then plated for viability and mutation determinations. At least 16 independent mutation frequencies were determined for each. Mutation rates were calculated by the method of Drake (6).