Endonuclease III（nth) is a DNA repair enzyme which has both DNA N-glycosylase activity and AP-lyase activity. The DNA N-glycosylase activity releases numerous damaged pyrimidines from DNA by cleaving the N-glycosidic bond and leaving an AP（apurinic/apyrimidinic) site. This AP-lyase activity cleaves the phosphodiester bond 3’ to the AP site by a beta-elimination， thus leaving a 3’-terminal unsaturated sugar and a product with a terminal 5’-phosphate.
