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

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19 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)1061-1067
Number of pages7
JournalCell Reports
Issue number5
StatePublished - Nov 29 2012


ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)

Cite this

Chen, X. F., Lehmann, L., Lin, J. J., Vashisht, A., Schmidt, R., Ferrari, R., Huang, C., McKee, R., Mosley, A., Plath, K., Kurdistani, S. K., Wohlschlegel, J., & Carey, M. (2012). Mediator and SAGA Have Distinct Roles in Pol II Preinitiation Complex Assembly and Function. Cell Reports, 2(5), 1061-1067.