POLB-bound FEN1 (flap endonuclease) cleaves the displaced DNA strand (flap structure), which contains the damaged AP residue that could not be excised by POLB (DNA polymerase beta) (Klungland and Lindahl 1997, Prasad et al. 2001, Liu et al. 2005).
Vande Berg, BJ,
5'-flap endonuclease activity of FEN1:POLB:SSB(3'poly-dNMP-displaced 5'ddRP-FLAP)-dsDNA [nucleoplasm]