SUBSTRATE-SPECIFICITY OF THE OGG1 PROTEIN OF SACCHAROMYCES-CEREVISIAE- EXCISION OF GUANINE LESIONS PRODUCED IN DNA BY IONIZING-RADIATION OR HYDROGEN-PEROXIDE METAL-ION GENERATED FREE-RADICALS

We have investigated the substrate specificity of the Ogg1 protein of Saccharomyces cerevisiae (yOgg1 protein) for excision of modified DNA bases from oxidatively damaged DNA substrates using gas chromatography /isotope dilution mass spectrometry, Four DNA substrates prepared by t reatment with H2O2/Fe(III)-EDTA/ascorbic acid, H2O2/Cu(II) and gamma-i rradiation under N2O or air were used, The results showed that 8-hydro xyguanine (8-OH-Gua) and 2,6-diamino-4-hydroxy-5-formamidopyrimid (Fap y-Gua) were efficiently excised from DNA exposed to ionizing radiation in the presence of N2O or air, On the other hand, 8-OH-Gua and FapyGu a were not excised from H2O2/Fe(III)-EDTA/ascorbic acid-treated and H2 O2/Cu(II)-treated DNA respectively, Fourteen other lesions, including the adenine lesions 8-hydroxyadenine and 4,6-diamino-5-formamidopyrimi dine, were not excised from any of the DNA substrates. Kinetics of exc ision significantly depended on the nature of the damaged DNA substrat es. The findings suggest that, in addition to 8-OH-Gua, FapyGua may al so be a primary substrate of yOgg1 in cells, The results also show sig nificant differences between the substrate specificities of yOgg1 prot ein and its functional analog Fpg protein in Escherichia coli.