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 methylation in cancer lung cancers or non-small-cell lung cancer squamous cell carcinomas. The article Werner syndrome ATP-dependent helicase indicates the DNA repair gene "WRN" has a promoter that is frequently hypermethylated in a number of cancers, with hypermethylation occurring in 11% to 38% of colorectal, head and neck, stomach, prostate, breast, thyroid, non-Hodgkin lymphoma, chondrosarcoma and osteosarcoma cancers (see WRN). As discussed by Jin and Roberston in their review, silencing of a DNA repair gene by hypermethylation may be a very early step in progression to cancer. Such silencing is proposed to act similarly to a germ-line mutation in a DNA repair gene,