Subunit of TFIIH and nucleotide excision repair factor 3 complexes; involved in transcription initiation, required for nucleotide excision repair; RING domain hydrophobic loop is required for transcription start site scanning as part of TFIIK, the protein kinase component of TFIIH, at the interface with RNAPII in the pre-initiation complex; RING finger protein similar to mammalian CAK and TFIIH subunit