Proliferating cell nuclear antigen 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 epsilon (Pol ε) 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. Since DNA polymerase epsilon is involved in resynthesis of excised damaged DNA strands during
DNA re-replication and Cdc6 expression. Loss of p53 regulation in cells can also be observed frequently in cell lines that overexpress Cdt1 or Cdc6. For the special case of cell cycle-regulated DNA replication in which DNA synthesis is uncoupled from cell cycle progression refer to endoreduplication. Endoreduplication is an important and widespread mechanism in many cell types. It does not adhere to many of the cell cycle checkpoints and damage controls in regularly dividing cells, but it does not result in uncontrolled re-replication. Endoreduplication is a controlled process and occurs to perform a specific cell function. In some cells, it has been