This antibody is useful for identifying the expression of Proliferating Cell Nuclear Antigen (PCNA) or cyclin or polymerase delta auxiliary protein. It is elevated in the nucleus during late G1 phase immediately before the onset of DNA synthesis, becoming maximal during S-phase and declining during G2 and M phases. PCNA may act as an auxiliary protein of DNA polymerase-delta to play a fundamental role in the initiation of cell proliferation and may be useful when used in a panel of antibodies.