Bifunctional DNA N-glycosylase with associated apurinic/apyrimidinic (AP) lyase function that catalyzes the first step in base excision repair (BER), the primary repair pathway for the repair of oxidative DNA damage. The DNA N-glycosylase activity releases the damaged DNA base from DNA by cleaving the N-glycosidic bond, leaving an AP site. The AP-lyase activity cleaves the phosphodiester bond 3' to the AP site by a beta-elimination. Primarily recognizes and repairs oxidative base damage of pyrimidines, but also purine-derived lesions, alkylation damage as well as abasic sites. Can also repair the oxidation products of 8-oxoguanine. 2'-deoxyribonucleotide-(2'-deoxyribose 5'-phosphate)-2'-deoxyribonucleotide-DNA = a 3'-end 2'-deoxyribonucleotide-(2,3-dehydro-2,3-deoxyribose 5'-phosphate)-DNA + a 5'-end 5'-monophospho-2'-deoxyribonucleoside-DNA + H(+) Binds 1 [4Fe-4S] cluster. The cluster does not appear to play a role in catalysis, but is probably involved in the proper positioning of the enzyme along the DNA strand. Interacts with MLH1. Exclusively nuclear and not responsive to changes in either nuclear or mitochondrial oxidative stress. Constitutively expressed. Monosumoylated. Greatly increases spontaneous and hydrogen peroxide-induced mutation frequency. Present with 125 molecules/cell in log phase SD medium. Belongs to the Nth/MutY family.