Constitutive activation of the SOS response, but not overexpression of RecA, restores UV resistance to uvrD303 cells. Filled squares, uvrD303 (SS5704); filled triangles, recAo281 (SS5962); filled circles, lexA::Tn5 (SS5959); open triangles, recAo281 uvrD303 (SS5963); open circles, lexA::Tn5 uvrD303 (SS5960). Survival was measured for untreated cells and at doses of 10, 20, and 60 J/m2 UV light. Each data point represents the average for at least three independent experiments. Error bars represent standard deviations.