Activator-Mediator binding regulates Mediator-cofactor interactions.
The 26-subunit, 1.2 MDa human Mediator complex is essential for expression of perhaps all protein-coding genes. Activator binding triggers major structural shifts within Mediator, suggesting a straightforward means to spatially and temporally regulate Mediator activity. By using mass spectrometry (MudPIT) and other techniques, we have compared the subunit composition of Mediator in three different structural states: bound to the activator SREBP-1a, VP16, or an activator-free state. As expected, consensus Mediator subunits were similarly represented in each sample. However, we identify a set of cofactors that interact specifically with activator-bound but not activator-free Mediator, suggesting activator binding triggers new Mediator-cofactor interactions. Furthermore, MudPIT combined with biochemical assays reveals a nonoverlapping set of coregulatory factors associated with SREBP-Mediator vs. VP16-Mediator. These data define an expanded role for activators in regulating gene expression in humans and suggest that distinct, activator-induced structural shifts regulate Mediator function in gene-specific ways.
Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309, USA.
Christopher C
CC
Ebmeier
Dylan J
DJ
Taatjes
D001671:Biochemistry / Q000379:methods; D002467:Cell Nucleus / Q000378:metabolism; D002843:Chromatin / Q000737:chemistry; D002853:Chromatography, Liquid / Q000379:methods; D056850:Cyclin-Dependent Kinase 8 / Q000737:chemistry; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006367:HeLa Cells; D017405:Herpes Simplex Virus Protein Vmw65 / Q000737:chemistry; D006801:Humans; D013058:Mass Spectrometry / Q000379:methods; D056892:Mediator Complex / Q000378:metabolism / Q000502:physiology*; D008954:Models, Biological; D011485:Protein Binding; D051780:Sterol Regulatory Element Binding Protein 1 / Q000737:chemistry
D002843:Chromatin; D017405:Herpes Simplex Virus Protein Vmw65; D056892:Mediator Complex; D051780:Sterol Regulatory Element Binding Protein 1; C095686:CDK8 protein, human; D056850:Cyclin-Dependent Kinase 8