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#base excision repair

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Repair Pathway

Gap filling during BER in prokaryotes is done by

In prokaryotes short-patch base excision repair gap filling after AP incision and dRP removal requires polymerase capable of single-nucleotide insertion and possessing 5'→3' exonuclease for nick translation. DNA Polymerase I encoded by polA fulfills roles: its polymerase domain inserts correct nucleotide using undamaged complementary strand as template, while 5'→3' exonuclease removes downstream 5' dRP or flap. DNA Pol III is major replicase unsuitable for repair synthesis, Pol II participates in SOS lesion bypass, and Pol β is eukaryotic counterpart of Pol I lacking in prokaryotes, highlighting Pol I's central repair function.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 5: DNA Pol I in Prokaryotic BER Gap Filling

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Repair Pathway

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

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