PCNA (Proliferating Cell Nuclear Antigen) is found in the nucleus and is a cofactor of DNA polymerase delta. This protein is associated with DNA synthesis and repair. The encoded protein acts as a homotrimer and helps increase the processivity of leading strand synthesis during DNA replication. It appears during late G1- phase, S-phase of mitosis and persists until the end of the M-phase because of its long biological half-life.