ERCC3 and xeroderma pigmentosum: NER is initiated by recognition of the damage by replication protein A (RPA) and xeroderma pigmentosum, removal of the single-stranded fragment by transcription factor II H (TFIIH, containing ATP-dependent DNA helicases XPB and XPD) and XPF-ERCC1 and XPG endonucleases, synthesis of the complementary sequence by replication factor C (RFC), PCNA and (Pol δ/ε/κ) and ligation by LIG1/FEN1 or LIG3/XRCC1 to form a double-stranded DNA.