Apurinic endonuclease activity of yeast Apn2 protein

Abasic (apurinic/apyrimidinic; AP) sites are generated in vivo through spon taneous base loss and by enzymatic removal of bases damaged by alkylating a gents and reactive oxygen species, In Saccharomyces cerevisiae, the APN1 an d APN2 genes function in alternate pathways of AP site removal. Apn2-like p roteins have been identified in other eukaryotes including humans, and thes e proteins form a distinct subfamily within the exonuclease III (ExoIII)/Ap e1/Apn2 family of proteins. Apn2 and other members of this subfamily contai n a carboxyl-terminal extension not present in the ExoIII/Ape1-like protein s. Here, we purify the Apn2 protein from yeast and show that, it is a class II AP endonuclease. Deletion of the carboxyl terminus does not affect the AP endonuclease activity of the protein, but this protein is defective in t he removal of AP sites in vivo. The carboxyl terminus may enable Apn2 to co mplex with other proteins, and such a multiprotein assembly may be necessar y for the efficient recognition and cleavage of AP sites in vivo.