Proliferating cell nuclear antigen (PCNA)

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.

Must be loaded onto DNA in order to be able to stimulate APEX2. Plays a vital role in DNA damage response (DDR) by being conveniently positioned in the replication fork to coordinate DNA replication with DNA repair and DNA damage tolerance pathways (PubMed:24939902).