Apurinic/apyrimidinic (AP) sites (pre-mutagenic lesions encoded by the APEX1 gene that can prevent normal DNA replication) occur frequently in DNA molecules by spontaneous hydrolysis, by DNA damaging agents or by DNA glycosylases that remove specific abnormal bases.
Apurinic/apyrimidinic (AP) sites (also called "abasic sites") occur frequently in DNA molecules by spontaneous hydrolysis, by DNA damaging agents or by DNA glycosylases that remove specific abnormal bases. AP sites are pre-mutagenic lesions that can prevent normal DNA replication. DNA-(apurinic or apyrimidinic site) lyase is an enzyme that in humans is encoded by the APEX1 gene. 
