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
| Experiment | lac allele (mutation) | Genotype | lac orientation | Lac+/108 | L/R ratio* | Rifr/108 |
|---|---|---|---|---|---|---|
| 1 | CC104 | mutL | L | 3.0 | 1.9 (0.005) | 110 |
| (G⋅C→T⋅A) | mutL | R | 1.6 | 90 | ||
| recA730, mutL | L | 5.0 | 0.45 (0.0002) | 260 | ||
| recA730, mutL | R | 11 | 270 | |||
| 2 | CC105 | mutL | L | 1.2 | 4.0 (0.007) | 49 |
| (A⋅T→T⋅A) | mutL | R | 0.3 | 54 | ||
| recA730, mutL | L | 6.7 | 0.08 (<0.0001) | 280 | ||
| recA730, mutL | R | 79 | 280 | |||
| 3 | CC106 | mutL | L | 1.2 | 0.25 (0.002) | 130 |
| (A⋅T→G⋅C) | mutL | R | 4.8 | 140 | ||
| recA730, mutL | L | 18 | 1.3 (0.90) | 590 | ||
| recA730, mutL | R | 14 | 610 |
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.