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 DNA damage tolerance pathway known as post-replication repair (PRR). In PRR, there are two sub-pathways: (1) a translesion pathway, which is carried out by specialised DNA polymerases that are able to incorporate damaged DNA bases into their active sites (unlike the normal replicative polymerase, which stall), and hence bypass the damage, and (2) a proposed "template switch" pathway that is thought to involve damage bypass by recruitment of the homologous recombination machinery. PCNA is pivotal to the activation of these pathways and the choice as to which pathway is utilised by the cell. PCNA becomes post-translationally modified by ubiquitin. Mono-ubiquitin of lysine number 164 on PCNA activates the translesion synthesis pathway. Extension of this mono-ubiquitin by a non-canonical lysine-63-linked poly-ubiquitin chain on PCNA is thought to activate the template switch pathway. Furthermore, sumoylation (by small ubiquitin-like modifier, SUMO) of PCNA lysine-164 (and to a lesser extent, lysine-127) inhibits the template switch pathway. This antagonistic effect occurs because sumoylated PCNA recruits a DNA helicase called Srs2, which has a role in disrupting Rad51 nucleoprotein filaments fundamental for initiation of homologous recombination.
Read more about this topic: Proliferating Cell Nuclear Antigen
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