Multifunctional RNA polymerase II initiation factor δ from rat liver: Relationship between carboxyl-terminal domain kinase, ATPase, and DNA helicase activities

RNA polymerase II initiation factor δ was previously purified from rat liver and found to possess a closely associated DNA-dependent ATPase activity and a protein kinase activity capable of phosphorylating the carboxyl-terminal domain (CTD) of the largest subunit of RNA polymerase II (Serizawa, H., Conaway, R. C., and Conaway, J. W. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 7476-7480). In addition, δ's human homolog, BTF2(TFIIH), was recently shown to have an associated DNA helicase activity (Schaeffer, L., Roy, R., Humbert, S., Moncollin, V., Vermeulen, W., Hoeijmakers, J. H. J., Chambon, P., and Egly, J.-M. (1993) Science 259, 58-63). Here we demonstrate that initiation factor δ also possesses DNA helicase activity. In addition, we compare the properties of δ's associated CTD kinase, ATPase, and DNA helicase activities. Whereas the enzymatic properties of ATPase and DNA helicase are similar and consistent with the possibility that they could function in ATP-dependent activation of the preinitiation complex, ATPase and CTD kinase exhibit significant differences in their nucleotide specificities, responses to DNA effectors, and sensitivities to inhibitors.