Base excision repair is initiated by removal of
Base excision repair handles small non-helix-distorting lesions such as deaminated bases, oxidized bases, and alkylated bases. Pathway initiates with lesion-specific DNA glycosylase scanning minor groove hydrolyzing N-glycosidic bond linking damaged base to deoxyribose, leaving apurinic-apyrimidinic site with intact phosphodiester backbone. Monofunctional glycosylases generate AP site requiring AP endonuclease incision; bifunctional glycosylases additionally possess AP lyase activity. Removal strictly of base not nucleotide maintains backbone continuity distinguishing BER from NER which excises oligonucleotide segment containing distortion, allowing precise replacement of single nucleotide patch.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 5: BER Initiation by Damaged Base Removal