DNA repair enzyme that cleaves apurinic/apyrimidinic (AP) sites and removes 3'-blocking groups present at single strand breaks of damaged DNA. APN1 accounts for > 97% of both apurinic/apyrimidinic (AP) endonuclease and DNA 3'-repair diesterase activities. Binds 3 Zn(2+) ions. Monomer. Present with 7250 molecules/cell in log phase SD medium. Belongs to the AP endonuclease 2 family.