This gene encodes a subunit of transcription/repair factor TFIIH, which functions in gene transcription and DNA repair. This protein stimulates ERCC3/XPB ATPase activity to trigger DNA opening during DNA repair, and is implicated in regulating cellular levels of TFIIH. Mutations in this gene result in trichothiodystrophy, complementation group A. [provided by RefSeq, Mar 2009].