修复单个核苷酸受伤位点。这些小的损伤位点不能被uvrABC系统识别。

(1) AP内切酶( AP endonuclease)修复系统 (2) GO系统

Base excision repair is the simplest version of DNA repair system the cells have. It is used to repair minor damages in DNA. DNA bases are modified due to deamination or alkylation. When there are base damages, DNA glycosylase recognizes and activates the base excision repair system and recover it with the help of enzymes AP endonuclease, DNA polymerase, and DNA ligase. Following steps are involved in BER system.

1. Recognition and removal of an incorrect or damaged base by a DNA glycosylase to create an abasic site (sites of base loss –apiurinic or apyrimidinic sites).
2. Abasic site incision by an apurinic/apyrimidinic endonuclease
3. Removal of the remaining sugar fragment by a lyase or phosphodiesterase
4. Gap filling by a DNA polymerase
5. Sealing of the nick by a DNA ligase