Role of deoxyribonucleic acid polymerases and deoxyribonucleic acid ligase in x-ray-induced repair synthesis in toluene-treated Escherichia coli K-12

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Abstract
Toluene-treated E. coli mutants were used to study the roles of DNA polymerases I, II and III, and of DNA ligase in repair synthesis and strand rejoining following X-irradiation. In cells possessing all 3 DNA polymerases, a greater amount of repair synthesis (exaggerated repair synthesis) and a failure of ligation are observed when DNA ligase activity is inhibited. In a mutant lacking the polymerizing activity of DNA polymerase I, exaggerated repair synthesis is not observed and strand rejoining does not occur even if DNA ligase is fully activated. In a mutant possessing the polymerizing activity of DNA polymerase I but lacking its 5'' .fwdarw. 3'' exonuclease activity, exaggerated repair synthesis is minimal. After irradiation, DNA polymerases II and III are capable of carrying out an ATP-dependent repair synthesis, but rejoining a strand breaks does not occur and exaggerated synthesis is not seen whether DNA ligase is active or not. DNA polymerase I and DNA ligase may act together to limit repair synthesis after X irradiation and both are apparently necessary in toluene-treated cells for strand rejoining. DNA polymerases II and III apparently cannot complete chain elongation and gap filling, and therefore repair carried out by these enzymes does not respond to ligase action.