Essential contributors to NER include the seven xeroderma pigmentosum (XP) complementation groups, spanning from XPA to XPG proteins, as well as the excision repair cross-complementing group 1 protein (ERCC1), the human counterpart of yeast RAD23 (hHR23B), the replication protein A (RPA), the subunits of the transcription factor with helicase activity (TFIIH), and the Cockayne syndrome proteins A and B (CSA and CSB) [30]. Here, XPA is linked to xeroderma pigmentosum.