EFFECT OF DNA-REPAIR ENZYMES ON MUTAGENESIS BY OXYGEN-FREE RADICALS

Cytosine to thymine transitions are among the most common types of mut ations produced by oxygen damage to DNA. One possible mechanism for th ese transitions is deamination of cytosine to uracil. Using both a for ward mutation assay as well as a reversion assay specific for damage t o cytosines we show that direct deamination to uracil does not play a significant role in mutagenesis induced by reactive oxygen free radica ls. In contrast, lesions sensitive to repair by E. coli endonuclease I II play a major role in oxidative mutagenesis as evidenced by the abil ity of endonuclease III to modulate the extent of mutagenesis that res ults from exposure of DNA to oxygen free radicals.