Polymerase delta complex (POLD) or polymerase epsilon complex (POLE) bound to PCNA-associated replication complex that also includes RPA and RFC complexes, catalyzes DNA strand displacement synthesis in a reaction facilitated by FEN1 and APEX1. POLD or POLE extend the 3' end of the single strand break (SSB) by adding up to 10 nucleotides. The 5' end of the SSB, which contains the oxidatively damaged AP (apurinic/apyrimidinic) dideoxyribose phosphate residue (5'ddRP) that could not be excised by POLB, is displaced as a flap structure by the joint action of FEN1 and POLD or POLE (Klungland and Lindahl 1997, Stucki et al. 1998, Dianov et al. 1999, Podlutsky et al. 2001, Ranalli et al. 2002).