The 6 exon PCNA gene at 20p12.3 codes for the 261 amino acid proliferating cell nuclear antigen. This can be regarded as a central scaffold that coordinates the assembly of replication and repair proteins at the DNA replication fork. It is an auxiliary protein of DNA polymerase delta and is involved in the control of eukaryotic DNA replication by increasing the polymerase's processibility during elongation of the leading strand. It plays a key role in DNA damage response as it coordinates DNA replication with DNA repair and DNA damage tolerance pathways. In this context it acts as a loading platform to recruit proteins that allow completion of DNA replication after DNA damage and promotes post-replication repair. Mutations of the gene are a cause of an ataxia telangiectasia syndrome(ataxia-telangiectasia-like disorder 2, ATLD2) with developmental delay, sensorineural hearing loss, short stature, and photosensitivity.