TABLE 4.

Mutator effect of amino acid substitutions in dnaE codon 655 carried on a plasmid in a dnaE⁺ host^a

Substitution encoded by plasmid	Mutation frequency (106)
	Lac−→Lac+	Rifs→Rifr
None (no plasmid)	0.24	0.01
None (Lys)	0.25	0.02
Arg	1.88	0.3
Ala	0.76	0.14
Asn	1.3	1.34
Asp	0.23	0.02
Gly	0.33	0.021
Tyr	21.9	8.45

^aPlasmids containing mutant dnaE1338 alleles were transformed into BS40/F′CC107 and selected for ampicillin resistance. Purified cultures were grown overnight in 1.5 ml of LB medium at 37°C and plated at 40°C for the determination of mutation.