THE SYNERGISTIC ACTION OF ULTRAVIOLET AND X RADIATION ON MUTANTS OF ESCHERICHIA COLI K‐12

Abstract— Prior UV irradiation increased the X‐ray sensitivity of wild‐type E. coli K‐12. This synergistic effect of combined UV and X irradiation was also observed, but to a reduced extent, in uvrA, uvrB, uvrC, and polA mutants, but was absent in exrA, recA, recB, or recC mutants of E. coli K‐12. Alkaline sucrose gradient studies demonstrated that the wand err gene‐controlled, growth‐medium‐dependent (Type III) repair of X‐ray‐induced DNA single‐strand breaks was inhibited by prior UV irradiation. This inhibition probably explains the synergistic effect of these two radiations on survival.