DNA repair enzyme that cleaves apurinic/apyrimidinic (AP) sites and removes 3'-blocking groups present at single strand breaks of damaged DNA. Provides the majority of the AP-endonuclease (APE) activity. Repairs phleomycin D1-induced DNA damage. Plays a role in oxidative damage repair. Exonucleolytic cleavage in the 3'- to 5'-direction to yield nucleoside 5'-phosphates. Probably binds two magnesium or manganese ions per subunit. Belongs to the DNA repair enzymes AP/ExoA family.