APN1 and APN2 encode multi-functional enzymes involved in the repair of damaged bases in DNA (reviewed in 4 and 5). Both Apn1p and Apn2p possess an apurinic/apyrimidinic (AP) endonuclease activity, a 3'-diesterase activity, and a 3' to 5' exonuclease activity (6, 7, 3). However, Apn1p constitutes the major apurinic/apyrimidinic (AP) endonuclease and 3'-phosphodiesterase in vivo, constituting close to 97% of these activities (6). During base excision repair (BER), the AP-endonuclease activity nicks the 5' side of abasic sites that are generated by the removal of oxidized and alkylated bases. This creates a single-strand break that contains a 3' hydroxyl group in preparation for DNA synthesis (8, 3). The 3'-phosphodiesterase activity is able to remove a wide range of 3' moieties at end of single-strand breaks in order to generate a 3' hydroxyl group (9, 7). The 3' to 5' exonuclease activity removes single nucleotides at a nick, such as 8oxodGMP that is mispaired with adenine/cytosine, leaving a single-nucleotide gap (10, 11, 7).

APN2 represents an alternate pathway for the repair of abasic sites. Although the methyl-methane sulfonate (MMS) sensitivity of apn2 single mutant strains are similar to wild-type strains, an apn1 apn2 double mutant is extremely sensitive (1). APN2 expression is induced six-fold in response to MMS (2).

Apn2p has sequence similarity to E. coli exonuclease III, S. pombe Apn2, and human Ape1 and Ape2 (1, 3, 12).

Last updated: 2006-10-26