Auxiliary protein of DNA polymerase delta and 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.