The endonucleases XPF/ERCC1 (xeroderma pigmentosum complementation group F/excision repair cross-complementation group 1) and XPG (xeroderma pigmentosum complementation group G) make the incision on both sides of the damaged strand and DNA polymerases δ and ε associated with RFC (replication factor C) and PCNA, respectively, are able to perform the gap-filling synthesis [73,74]. This evidence concerns the gene PCNA and xeroderma pigmentosum.