Table 1.

Spontaneous mutant frequencies in cells with various mutant polymerases

Genotype*	Spontaneous mutants/ 106 cells†
	RifR‡	NalR§
polB+dnaE+
polBΔ1 dnaE+
polB+dnaE915
polBΔ1 dnaE915
polB+dnaE+		ND
polBex1 dnaE+		ND
polB+dnaE911		ND
polBex1 dnaE911		ND

ND, not determined. 

^*Genotype corresponds to isogenic parental strains for top and bottom half of table, respectively. 

^†Medians of 15 independent cultures from 2–3 isolates each, grown in rich medium (top half of table) and minimal medium (bottom half of table). Errors represent 95% confidence intervals for the medians. 

^‡Mutations from rifampicin sensitivity to rifampicin resistance. 

^§Mutations from nalidixic acid sensitivity to nalidixic acid resistance.