MCM Proteins Are Associated with RNA Polymerase II Holoenzyme

Abstract

MCMs are a family of proteins related to ATP-dependent helicases that bind to origin recognition complexes and are required for initiation of DNA replication. We report that antibodies against MCM2(BM28) specifically inhibited transcription by RNA polymerase II (Pol II) in microinjected Xenopus oocytes. Consistent with this observation, MCM2 and other MCMs copurified with Pol II and general transcription factors (GTFs) in high-molecular-weight holoenzyme complexes isolated from Xenopus oocytes and HeLa cells. Pol II and GTFs also copurified with MCMs isolated by anti-MCM3 immunoaffinity chromatography. MCMs were specifically displaced from the holoenzyme complex by antibody against the C-terminal domain (CTD) of Pol II. In addition, MCMs bound to a CTD affinity column, suggesting that their association with holoenzyme depends in part on this domain of Pol II. These results suggest a new function for MCM proteins as components of the Pol II transcriptional apparatus.

ACKNOWLEDGMENTS

We thank N. Fong, M. Pandes, E. Lees, L. Rothblum, R. Roeder, N. Thompson, G. Evan, J.-M. Egly, and R. Wood for gifts of antibodies and J. Douglas, Dept. of Comparative Medicine, University of Toronto, and the ICRF animal unit for supplying Xenopus oocytes. We are also grateful to J. Greenblatt, J. Diffley, S. Mason, B. McNeil, J. Parvin, E. Rosonina, A. Wildeman, D. Evans, and A. Hilliker for valuable discussions and T. Boudreau for secretarial help.

This work was supported by a start-up grant to K.Y. from the University of Guelph and by grants to D.L.B. from the Medical Research Council of Canada and NIH GM-58613-01.