Component of the core-TFIIH basal transcription factor involved in nucleotide excision repair (NER) of DNA and, when complexed to CAK, in RNA transcription by RNA polymerase II. The N-terminus interacts with and regulates XPD whereas an intact C-terminus is required for a successful escape of RNAP II form the promoter.Humbert S., EMBO J. 13:2393-2398(1994).The MGC Project Team, Genome Res. 14:2121-2127(2004).van der Steege G., Eur. J. Hum. Genet. 3:87-95(1995).