Action of hydrogen peroxide on degradation of DNA after irradiation in Escherichia coli

Hydrogen peroxide (H2O2), which produces breaks in cellular DNA, has not hitherto been shown to cause degradation of DNA. In this investigation it was shown that if transcription was blocked with rifampin, treatment with H2O2 caused degradation of DNA to nearly the same extent as did γ-radiation. Further, if cells were given a treatment with H2O2 and incubated for 50 min, the amount of degradation in a second treatment was markedly less. This has been attributed to the induction of the inhibitor of post-irradiation degradation of DNA (prd) by the first treatment. There is thus a double action of H2O2: first, to induce inhibition, and second, to cause degradation of DNA to begin in non-induced cells. The genetic dependence of induction by H2O2 mimicked that of ionizing radiation. Accordingly, the induction process did not occur in recA- and lex- cells, because they were not inductible and was absent in recB- cells because they lacked exonuclease V, the major component of prd. Potassium iodide (KI), and OH radical scavenger, negated the action of peroxide on DNA. The results obtained in this study suggest a possible theory for the evolution of radiation response systems. (author)