Component of the general transcription and DNA repair factor IIH (TFIIH) core complex, which is involved in general and transcription-coupled nucleotide excision repair (NER) of damaged DNA and, when complexed to CAK, in RNA transcription by RNA polymerase II. In NER, TFIIH acts by opening DNA around the lesion to allow the excision of the damaged oligonucleotide and its replacement by a new DNA fragment. In transcription, TFIIH has an essential role in transcription initiation. When the pre-initiation complex (PIC) has been established, TFIIH is required for promoter opening and promoter escape. Phosphorylation of the C-terminal tail (CTD) of the largest subunit of RNA polymerase II by the kinase module CAK controls the initiation of transcription. Component of the 7-subunit TFIIH core complex composed of XPB/ERCC3, XPD/ERCC2, GTF2H1, GTF2H2, GTF2H3, GTF2H4 and GTF2H5, which is active in NER. The core complex associates with the 3-subunit CDK-activating kinase (CAK) module composed of CCNH/cyclin H, CDK7 and MNAT1 to form the 10-subunit holoenzyme (holo-TFIIH) active in transcription. Belongs to the TFB2 family.