The damage-inducible (din) genes of Escherichia coli are induced by various genotoxins in a different way

The SOS response of Escherichia coli strains carrying the lacZ gene fused t o the polB (dinA), dinB or dinD gene were investigated after treatment with several chemical agents and gamma-radiation. The induction levels of polB: :lacZ reached levels between 4.0- and 9.0-fold 120 min after treatment with nalidixic acid, H2O2 or ethanol. Pentachlorophenol did not significantly i nduce any din genes. gamma-Irradiation is not an inducer of polB and ethano l failed to induce dinB::lacZ and dinD::lacZ. Following irradiation with a dose of 10 Gy the responses of dinB and dinD were induced about 2.5 similar to 3.0-fold above non-irradiated dinB and dinD. We found that the response s of din::lacZ fusion genes to these genotoxins are induced in a dose-depen dent manner. The polB gene showed antagonistic responses to the simultaneou s treatment of nalidixic acid and H2O2 or nalidixic acid and ethanol. In ad dition, dinB and dinD in the presence of both nalidixic acid and H2O2 at th e same time showed no synergistic responses.