Short-patch and long-patch BER pathways. The figure illustrates the short-and long-patch pathways of BER. In both pathways, a DNA glycosylase initiates the repair by recognizing and removing a damaged base, leaving an AP site. APE1 subsequently cleaves the DNA backbone at the AP site, resulting in a single-strand break. In the short-patch pathway (left), XRCC1 forms a complex with Pol β and LIG3 to replace the damaged nucleotide and seal the nick. In the long-patch pathway (right), PCNA and PARP1 are recruited to the repair site. Pol δ/ε extends the repair patch by displacing the damaged strand. FEN1 then cleaves the displaced flap, and LIG1 seals the remaining nick to complete the repair.
