Action of Hydrogen Peroxide on Degradation of DNA after Irradiation in Escherichia Coli

Summary

Hydrogen peroxide (H₂O₂), which produces breaks in cellular DNA, has not hitherto been shown to cause degradation of DNA. In this investigation it is shown that if transcription is blocked with rifampin, treatment with H₂O₂ causes degradation of DNA to nearly the same extent as does gamma-radiation. Further, if cells are given a treatment with H₂O₂ and incubated for 50 min, the amount of degradation in a second treatment is markedly less. This is 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 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. Potassium iodide (KI), an OH radical scavenger, negates the action of peroxide on DNA. The results obtained in this study suggest a possible theory for the evolution of radiation response systems.