Table 2

Mutant frequencies (lac+ mutants per 108 cells) in SOS-induced pairs of strains containing the lac operon in opposite (L and R) orientations and carrying plasmid pRW134 (umuD′C)

Experimentlac allele (mutation)Relevant genotypelac orientationLac+/108L/R ratio(P value)*
1CC104 (G⋅C→T⋅A) mutL L0.91.2(0.53)
R0.75
recA730, mutL L4.70.36(0.003)
R13
mutL [pRW134]L1.01.7(0.09)
R0.6
recA730, mutL [pRW134]L7.60.18(<0.0001)
R43
2CC105 (A⋅T→T⋅A) mutL L0.52.5(0.02)
R0.2
recA730, mutL L5.30.095(<0.0001)
R56
mutL [pRW134]L0.92.3(0.50)
R0.4
recA730, mutL [pRW134]L170.11(<0.0001)
R151
  •  The experiments were performed with strains of the MC4100 background (see Materials and Methods). 

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