MMS sensitivity of the mutant and complementation by other infB alleles.
A) GTN1114 del(argA)743::kan (GTN1156) and GTN1115 del(argA)743::kan (GTN1157) bearing pSPCnusAinfB plasmids that contain infB(wt), infB(del1) (1), infB(del1) (2/3), or infB(del2/3,D409E) (2/3,409), or no infB (vec) allele. The asterisk (*) indicates that the strain required 40–42 h incubation (37°C) on MMS plates to yield sufficiently large colonies that could be counted, indicating especially slow growth on these plates (all other strains required 16–20 h incubation). The results are the average of 6–7 independent experiments. B) Multicopy infB(del2/3,D501N) allele can support growth in MMS provided that the chromosomal allele is not present. Viability of GTN932 infB(del1) del(infB)1::tet (GTN1114) and GTN932 del(infB)1::tet bearing the indicated pSPCnusAinfB plasmids (see the legend to panel A for the key) with and without MMS was determined (5–6 independent experiments). C) Sensitivity measured by 15-min exposure of cells at 6 mM and 18 mM MMS and plating in the absence of MMS (3–4 independent experiments). Strains with the indicated infB allele in the chromosome or transposon (<>) were used: GTN1050 (), GTN932 (wt), GTN1114 (<1>), GTN1115 (<2/3>), GTN1117 (<1> and del(priB)302), GTN381 (wt and priA300), GTN1323 (<1> and priA300), and GTN1376 (wt and recA938).