title: Mediator and SAGA have distinct roles in Pol II preinitiation complex assembly and function.
abstract: 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.
authors.affiliation: 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.
authors.forename: Xiao-Fen
authors.initials: XF
authors.lastname: Chen
authors.forename: Lynn
authors.initials: L
authors.lastname: Lehmann
authors.forename: Justin J
authors.initials: JJ
authors.lastname: Lin
authors.forename: Ajay
authors.initials: A
authors.lastname: Vashisht
authors.forename: Ryan
authors.initials: R
authors.lastname: Schmidt
authors.forename: Roberto
authors.initials: R
authors.lastname: Ferrari
authors.forename: Chengyang
authors.initials: C
authors.lastname: Huang
authors.forename: Robin
authors.initials: R
authors.lastname: McKee
authors.forename: Amber
authors.initials: A
authors.lastname: Mosley
authors.forename: Kathrin
authors.initials: K
authors.lastname: Plath
authors.forename: Siavash K
authors.initials: SK
authors.lastname: Kurdistani
authors.forename: James
authors.initials: J
authors.lastname: Wohlschlegel
authors.forename: Michael
authors.initials: M
authors.lastname: Carey
mesh_terms: D000818:Animals; D002460:Cell Line; D002843:Chromatin / Q000378:metabolism; D053595:Embryonic Stem Cells / Q000166:cytology / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D056892:Mediator Complex / Q000378:metabolism*; D051379:Mice; D011401:Promoter Regions, Genetic; D012319:RNA Polymerase II / Q000737:chemistry / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D035181:TATA-Box Binding Protein / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism*; D035362:Transcription Factor TFIID / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D002843:Chromatin; D056892:Mediator Complex; D012333:RNA, Messenger; D035181:TATA-Box Binding Protein; D015534:Trans-Activators; D035362:Transcription Factor TFIID; D012319:RNA Polymerase II