DNA synthesis in gamma-irradiated recombination deficient strains of ESCHERICHIA COLI

Summary: DNA synthesis in recA and recA exrA strains of Escherichia coli is strongly inhibited without delay by low doses of gamma-radiation. The synthesis that does occur in these strains appears to take place mainly on chromosomes that have not received a lethal hit. Low doses produce much less inhibition of DNA synthesis in exrA, recB, recA recB and wild-type strains. We conclude that the recA - gene product acts immediately, certainly before DNA replication, in the repair of lesions produced by gamma-irradiation. In recB bacteria the recA + gene product is not required for continued DNA synthesis, although the synthesis which occurs in recA recB strains may be abnormal since it is not reflected in increased survival. The exrA + gene product is not necessary for continued DNA replication, suggesting that its time of action in repair may be at a later stage.