A carboxyl-terminal-domain kinase associated with RNA polymerase II transcription factor δ from rat liver

We previously purified RNA polymerase II transcription factor δ from rat liver and found that it has an associated DNA-dependent ATPase (dATPase) activity. In this report, we show that δ is also closely associated with a protein kinase activity that catalyzes phosphorylation of the largest subunit of RNA polymerase II. Kinase activity copurifies with transcription and DNA-dependent ATPase (dATPase) activities when δ is analyzed by anion- and cation-exchange HPLC as well as by sucrose gradient sedimentation, arguing that δ possesses all three activities. Phosphorylation of the largest subunits of both rat and yeast RNA polymerase II is stimulated by DNA, whereas phosphorylation of a synthetic peptide containing multiple copies of the carboxyl-terminal heptapeptide repeat is not. Although both ATP and GTP appear to function as phosphate donors, GTP is utilized less than 10% as well as ATP. These findings suggest that δ may exert its action in transcription at least in part through a mechanism involving phosphorylation of the largest subunit of RNA polymerase II.