RPA1 and xeroderma pigmentosum: XPA to G (xeroderma pigmentosum groups A–G), ERCC1 (excision repair cross complementation group1), RPA1, RPA2 (replication protein A1, replication protein A2) are the main proteins in this pathway and there are two damage recognition arms of the NER pathway: global genome repair (GGR) and transcription-coupled repair (TCR).