Auxiliary protein of DNA polymerase delta and epsilon, is involved in the control of eukaryotic DNA replication by increasing the polymerase's processibility during elongation of the leading strand . Induces a robust stimulatory effect on the 3'-5' exonuclease and 3'-phosphodiesterase, but not apurinic-apyrimidinic (AP) endonuclease, APEX2 activities. Has to be loaded onto DNA in order to be able to stimulate APEX2. Plays a key role in DNA damage response (DDR) by being conveniently positioned at the replication fork to coordinate DNA replication with DNA repair and DNA damage tolerance pathways . Acts as a loading platform to recruit DDR proteins that allow completion of DNA replication after DNA damage and promote postreplication repair: Monoubiquitinated PCNA leads to recruitment of translesion (TLS) polymerases, while 'Lys-63'-linked polyubiquitination of PCNA is involved in error-free pathway and employs recombination mechanisms to synthesize across the lesion .
Subcellular locations: Nucleus
Colocalizes with CREBBP, EP300 and POLD1 to sites of DNA damage . Forms nuclear foci representing sites of ongoing DNA replication and vary in morphology and number during S phase . Co-localizes with SMARCA5/SNF2H and BAZ1B/WSTF at replication foci during S phase . Together with APEX2, is redistributed in discrete nuclear foci in presence of oxidative DNA damaging agents.