PCNA - STRUCTURE, FUNCTIONS AND INTERACTIONS

Proliferating cell nuclear antigen (PCNA) plays an essential role in n ucleic acid metabolism as a component of the replication and repair ma chinery. This toroidal-shaped protein encircles DNA and can slide bidi rectionally along the duplex. One of the well-established functions fo r PCNA is its role as the processivity factor for DNA polymerase delta and epsilon. PCNA tethers the polymerase catalytic unit to the DNA te mplate for rapid and processive DNA synthesis. In the last several yea rs it has become apparent that PCNA interacts with proteins involved i n cell-cycle progression which are not a part of the DNA polymerase ap paratus. Some of these interactions have a direct effect on DNA synthe sis while the roles of several other interactions are not fully unders tood. This review summarizes the structural features of PCNA and descr ibes the diverse functions played by the protein in DNA replication an d repair as well as its possible role in chromatin assembly and gene t ranscription. The PCNA interactions with different cellular proteins a nd the importance of these interactions are also discussed.