PCNA

Overview
Proliferating Cell Nuclear Antigen, commonly known as PCNA, is a protein that acts as a processivity factor for DNA polymerase delta in eukaryotic cells. It achieves this processivity by encircling the DNA, thus creating a topological link to the genome. It is an example of a DNA clamp.

Expression in the nucleus during DNA synthesis
PCNA was originally identified as an antigen that is expressed in the nuclei of cells during the DNA synthesis phase of the cell cycle . Part of the protein was sequenced and that sequence was used to allow isolation of a cDNA clone. PCNA helps hold DNA polymerase delta (Pol δ) to DNA. PCNA is clamped to DNA through the action of replication factor C (RFC), which is a heteropentameric member of the AAA+ class of ATPases. Expression of PCNA is under the control of E2F transcription factor-containing complexes.

Role in DNA repair
Since DNA polymerase delta is involved in resynthesis of excised damaged DNA strands during DNA repair, PCNA is important for both DNA synthesis and DNA repair. PCNA is also involved in the switch to DNA damage bypass translation synthesis.