Any enzyme that cleaves DNA on the 5′ side of a site in a DNA molecule that lacks a purine or pyrimidine. An AP site is a “hole” in a double-stranded DNA left by removal of a base, but leaving the sugar phosphate backbone intact. AP is the abbreviation for apurinic or apyrimidinic, referring to the loss of purines or pyrimidines. AP sites result when DNA glycosylases (q.v.) remove chemically altered bases from the polymer. An AP endonuclease will then break the phosphodiester backbone, and this allows excision of the damaged region. See cut-and-patch repair.
Subjects: Chemistry — Genetics and Genomics.