Table 1

Mutant frequencies in SOS-induced pairs of strains containing the lac operon in opposite (L and R) orientations on the E. coli chromosome

Experimentlac allele (mutation)Genotypelac orientationLac+/108L/R ratio*Rifr/108
1CC104 mutL L3.01.9 (0.005)110
(G⋅C→T⋅A) mutL R1.690
recA730, mutL L5.00.45 (0.0002)260
recA730, mutL R11270
2CC105 mutL L1.24.0 (0.007)49
(A⋅T→T⋅A) mutL R0.354
recA730, mutL L6.70.08 (<0.0001)280
recA730, mutL R79280
3CC106 mutL L1.20.25 (0.002)130
(A⋅T→G⋅C) mutL R4.8140
recA730, mutL L181.3 (0.90)590
recA730, mutL R14610
  •  These experiments were performed with strains of the NR11531 background (see Materials and Methods). Although between individual experiments lac and rif+ mutant frequencies sometimes vary significantly, the relative mutant frequencies within each experiment are generally very reproducible (see also ref. 27). 

  • * In parentheses, the P value indicates significance of L- vs. R-frequency differences, calculated as described in Materials and Methods.