Fig 2.

DinB site-directed derivatives are proficient for lesion bypass in vivo, and a C66A mutation eliminates hypersensitivity of the catalytically inactive dinB(D103N) strain. Survival of the ΔdinB strains (A) and ΔdinB ΔumuDC strains (B) is shown. In both backgrounds, expression of DinB(C66A) or DinB(P67A) does not affect survival in the presence of either NFZ (1.5 μg ml⁻¹) or MMS (7.5 mM). Cells expressing DinB(D103N) are highly sensitive to both DNA-damaging agents. However, the extreme sensitivity of cells expressing DinB(D103N) is suppressed in cells expressing the double mutant, DinB(C66A D103N), to levels similar to those of the vector-only strain, which is consistent with loss of catalytic activity. The NFZ survival shown for the DinB(C66A D103N) double mutant in the ΔdinB strain suggests that other DNA polymerases, e.g., DNA Pol V, might be responsible for the bypass; this is no longer the case in the ΔdinB ΔumuDC strain. The various dinB alleles are expressed from the native promoter in a low-copy-number vector (pYG768) (28). Three biological replicates were assessed for each strain. Means and 1 standard deviation (SD) are shown.