ERCC2 and xeroderma pigmentosum: During NER, transcription factor IIH (TFIIH) and replication protein A (RPA) bind sequentially to damaged DNA to enable single-stranded DNA stabilization, and subunits of TFIIH, xeroderma pigmentosum, and complementation group B (XPB) and group D (XPD) helicases then unwind the DNA double helix at the damaged site.