Catalytic component of the TFIIK complex (KIN28-CCL1 dimer) which is the protein kinase component of transcription factor IIH (TFIIH) and phosphorylates the C-terminal domain of RNA polymerase II during transition from transcription to elongation after preinitiation complex (PIC) formation, thereby positively regulating transcription. TFIIH (or factor B) is essential for both basal and activated transcription, and is involved in nucleotide excision repair (NER) of damaged DNA. TFIIH has DNA-dependent ATPase activity and is essential for polymerase II transcription in vitro. Essential for cell proliferation. [DNA-directed RNA polymerase] + ATP = ADP + H(+) + phospho-[DNA-directed RNA polymerase] CCL1 and KIN28 form the TFIIK complex, a component of the TFIIH holo complex. Component of a complex consisting of KIN28, CCL1 and TFB3. Interacts with TFB3. Also interacts with HNT1 and HOG1. Phosphorylation of Thr-162 regulates the affinity of interaction between CCL1, KIN28 and TFB3. Thr-162 phosphorylation does not vary through the cell cycle and is necessary for full kinase activity. Present with 4400 molecules/cell in log phase SD medium. Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. CDC2/CDKX subfamily.