Both 45- and 47-kDa subunits of TFIIK, a subcomplex of RNA polymerase II general transcription factor TFIIH, are encoded by the yeast cyclin gene CCL1. In all likelihood, these two subunits individually form cyclin-dependent kinase/cyclin dimers with Kin28 protein, a key enzyme in phosphorylation of the C-terminal domain of RNA polymerase II concomitant with transcription.