Proliferating cell nuclear antigen (PCNA) plays a crucial role in nucleic acid metabolism as it pertains to DNA replication and repair. Most noted for its activation of subunits of DNA polymerase, it has also been found to interact with cell-cycle progression proteins. Modifications of PCNA as a result of cellular response put PCNA in a pivotal position with DNA replication, DNA damage, and chromatin structure and function. In response to DNA damage, PCNA is ubiquitinated and becomes part of the RAD-6 dependent DNA repair pathway, where it acts as a substrate with a variety of p