Mediator and SAGA Have Distinct Roles in Pol II Preinitiation Complex Assembly and Function
Xiao-Fen Chen,
Lynn Lehmann,
Justin J. Lin,
Ajay Vashisht,
Ryan Schmidt,
Roberto Ferrari,
Chengyang Huang,
Robin McKee,
Amber Mosley,
Kathrin Plath,
Siavash K. Kurdistani,
James Wohlschlegel,
Michael Carey
Affiliations
Xiao-Fen Chen
Department of Biological Chemistry, David Geffen School of Medicine, University of California, BSRB 351A, 615 Charles E. Young Drive, Los Angeles, CA 90095-1737, USA
Lynn Lehmann
Department of Biological Chemistry, David Geffen School of Medicine, University of California, BSRB 351A, 615 Charles E. Young Drive, Los Angeles, CA 90095-1737, USA
Justin J. Lin
Department of Biological Chemistry, David Geffen School of Medicine, University of California, BSRB 351A, 615 Charles E. Young Drive, Los Angeles, CA 90095-1737, USA
Ajay Vashisht
Department of Biological Chemistry, David Geffen School of Medicine, University of California, BSRB 351A, 615 Charles E. Young Drive, Los Angeles, CA 90095-1737, USA
Ryan Schmidt
Department of Biological Chemistry, David Geffen School of Medicine, University of California, BSRB 351A, 615 Charles E. Young Drive, Los Angeles, CA 90095-1737, USA
Roberto Ferrari
Department of Biological Chemistry, David Geffen School of Medicine, University of California, BSRB 351A, 615 Charles E. Young Drive, Los Angeles, CA 90095-1737, USA
Chengyang Huang
Department of Biological Chemistry, David Geffen School of Medicine, University of California, BSRB 351A, 615 Charles E. Young Drive, Los Angeles, CA 90095-1737, USA
Robin McKee
Department of Biological Chemistry, David Geffen School of Medicine, University of California, BSRB 351A, 615 Charles E. Young Drive, Los Angeles, CA 90095-1737, USA
Amber Mosley
Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Room MS1021H, 635 Barnhill Drive, Indianapolis, IN 46202, USA
Kathrin Plath
Department of Biological Chemistry, David Geffen School of Medicine, University of California, BSRB 351A, 615 Charles E. Young Drive, Los Angeles, CA 90095-1737, USA
Siavash K. Kurdistani
Department of Biological Chemistry, David Geffen School of Medicine, University of California, BSRB 351A, 615 Charles E. Young Drive, Los Angeles, CA 90095-1737, USA
James Wohlschlegel
Department of Biological Chemistry, David Geffen School of Medicine, University of California, BSRB 351A, 615 Charles E. Young Drive, Los Angeles, CA 90095-1737, USA
Michael Carey
Department of Biological Chemistry, David Geffen School of Medicine, University of California, BSRB 351A, 615 Charles E. Young Drive, Los Angeles, CA 90095-1737, USA
A key feature of RNA polymerase II (Pol II) preinitiation complexes (PICs) is their ability to coordinate transcription initiation with chromatin modification and remodeling. To understand how this coordination is achieved, we employed extensive proteomic and mechanistic analyses to study the composition and assembly of PICs in HeLa cell and mouse embryonic stem cell (ESC) nuclear extracts. Strikingly, most of the machinery that is necessary for transcription initiation on chromatin is part of the PIC. The PIC is nearly identical between ESCs and HeLa cells and contains two major coactivator complexes: Mediator and SAGA. Genome-wide analysis of Mediator reveals that it has a close correlation with Pol II, TATA-binding protein, and messenger RNA levels and thus may play a major role in PIC assembly. Moreover, Mediator coordinates assembly of the Pol II initiation factors and chromatin machinery into a PIC in vitro, whereas SAGA acts after PIC assembly to allow transcription on chromatin.
