The apurinic-apyrimidinic endonuclease IV family of DNA repair enzymes.

Apurinic-apyrimidinic (AP) sites are DNA lesions that lack template information and are produced either spontaneously or by a variety of DNA damaging agents. AP sites must therefore be repaired; otherwise they are mutagenic. All cells investigated to date possess the DNA repair enzyme AP endonuclease that can repair AP sites. There are two discrete families of AP endonucleases, Exo III and Endo IV, which are exemplified by Escherichia coli exonuclease III and endonuclease IV, respectively. These AP endonucleases have evolved not only to repair AP sites but also to correct distinct DNA lesions.