PCNA is a nuclear protein essential for DNA replication as well as DNA excision and mismatch repair pathways. It coordinates the recruitment and association of needed components during both of these processes, both of which are essential for cell cycle regulation and cell response to stress. Through the symmetric association of three identical monomers, PCNA forms a toroidal, ring-shaped structure that encircles DNA. This serves as the scaffold upon which polymerases and other proteins dock and associate.
