A mediator was isolated from yeast that enabled a response to the activator proteins GAL4-VP16 and GCN4 in a transcription system reconstituted with essentially homogeneous basal factors and RNA polymerase II. The mediator comprised some 20 polypeptides, including the three subunits of TFIIF and other polypeptides cross-reactive with antisera against GAL11, SUG1, SRB2, SRB4, SRB5, and SRB6 proteins. Mediator not only enabled activated transcription but also conferred 8-fold greater activity in basal transcription and 12-fold greater efficiency of phosphorylation of RNA polymerase II by the TFIIH-associated C-terminal repeat domain (CTD) kinase, indicative of mediator-CTD interaction. A holoenzyme form of RNA polymerase II was independently isolated that supported a response to activator proteins with purified basal factors. The holoenzyme proved to consist of mediator associated with core 12-subunit RNA polymerase II.
Bibliographical noteFunding Information:
Correspondence should be addressed to R. D. K. We thank D. Bushnell, B. Cairns, J. Feaver, P. Flanagan, A. Gnatt, J. LaPointe, and J. Svejstrup for purified transcription proteins; A. Koleske, C. Thompson, and R. Young for anti-SRB antibodies; H. Sakurai and T. Fukasawa for anti-GAL1 1 antibody; J. Swaffield and S. Johnston for anti-SUGl antibody; P. A. Weil for yeast TAFs; and K. Leuther for helpful advice. S. B. is a recipient of a European Molecular Biology Organization long-term postdoctoral fellowship. M. H. S. was a recipient of an American Cancer Society (California Division) senior postdoctoral fellowship. This research was supported by National Institutes Health grant GM-36659 to R. D. K.
All Science Journal Classification (ASJC) codes
- Biochemistry, Genetics and Molecular Biology(all)