Action of Hydrogen Peroxide on Degradation of DNA after Irradiation inEscherichia Coli

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Abstract
H2O2, which produces breaks in cellular DNA, was not previously shown to cause degradation of DNA. If transcription is blocked with rifampin, treatment with H2O2 causes degradation of DNA to nearly the same extent as does .gamma.-radiation. If cells are given a treatment with H2O2 and incubated for 50 min, the amount of degradation in a 2nd treatment is markedly less. This is attributed to the induction of the inhibitor of post-irradiation degradation of DNA (prd) by the 1st treatment. There is a double action of H2O2: to induce inhibition, and to cause degradation of DNA to begin in non-induced cells. The genetic dependence of induction by H2O2 mimics that of ionizing radiation. Accordingly, the induction process does not occur in recA- and lex- cells, because they are not inducible, and is absent in recB- cells because they lack exonuclease V, the major component of prd. KI, an OH radical scavenger, negates the action of peroxide on DNA. A possible theory for the evolution of radiation response systems is suggested.