Endonuclease IV plays a role in DNA repair. It cleaves phosphodiester bonds at apurinic or apyrimidinic (AP) sites, generating a 3'-hydroxyl group and a 5'-terminal sugar phosphate. It preferentially attacks modified AP sites created by bleomycin and neocarzinostatin. Endonucleolytic cleavage to 5'-phosphooligonucleotide end-products. Binds 3 Zn(2+) ions. Can also bind Mn(2+) ions. Monomer. Endonuclease IV is induced by agents which generate superoxide radical anions. Belongs to the AP endonuclease 2 family.