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 (PubMed:16782061, PubMed:20410075). In addition, possesses a 3'-5' exonuclease activity (PubMed:16782061). Endonucleolytic cleavage to 5'-phosphooligonucleotide end-products. Binds 3 Zn(2+) ions. Belongs to the AP endonuclease 2 family. Back et al. found that TthNfo also catalyzes the excision of uracil from DNA, but further protein analysis by Schomacher et al. show that it does not exhibit DNA uracil glycosylase activity or DNA uridine endonuclease activity.