Acts as component of the general transcription and DNA repair factor IIH (TFIIH or factor B), which is essential for both basal and activated transcription, and is involved in nucleotide excision repair (NER) of damaged DNA. TFIIH has CTD kinase activity and DNA-dependent ATPase activity, and is essential for polymerase II transcription (By similarity). One of the nine subunits forming the core-TFIIH basal transcription factor. Interacts also with skp1 and with the mcs2-mcs6 complex.