Overview:

PCNA is a nuclear protein whose appearance correlates with the proliferative state of the cells and is a cofactor of DNA polymerase delta. PCNA is a homotrimer and helps increase the processivity of leading strand synthesis during DNA replication. In response to DNA damage, PCNA is ubiquitinated and is involved in the RAD6-dependent DNA repair pathway. Immunofluorescence studies have shown that p300 may play a role in DNA repair synthesis through its interaction with PCNA. In vitro and in vivo p300 forms a complex with PCNA that does not depend on the S phase of the cell cycle and stimulates DNA synthesis in vitro (1). PCNA interacts with the Williams syndrome transcription factor (WSTF) allowing it to target to DNA replication foci, that then allows recruitment of SNF2H (2).

References:

1. Hasan, S. et al: Transcription coactivator p300 binds PCNA and may have a role in DNA repair synthesis. Nature 410: 387-391, 2001. 

2. Poot, R. A.et al: The Williams syndrome transcription factor interacts with PCNA to target chromatin remodelling by ISWI to replication foci. Nature Cell Biol. 6: 1236-1244, 2004.