title: The human CDK8 subcomplex is a molecular switch that controls Mediator coactivator function.
abstract: The human CDK8 subcomplex (CDK8, cyclin C, Med12, and Med13) negatively regulates transcription in ways not completely defined; past studies suggested CDK8 kinase activity was required for its repressive function. Using a reconstituted transcription system together with recombinant or endogenous CDK8 subcomplexes, we demonstrate that, in fact, Med12 and Med13 are critical for subcomplex-dependent repression, whereas CDK8 kinase activity is not. A hallmark of activated transcription is efficient reinitiation from promoter-bound scaffold complexes that recruit a series of pol II enzymes to the gene. Notably, the CDK8 submodule strongly represses even reinitiation events, suggesting a means to fine tune transcript levels. Structural and biochemical studies confirm the CDK8 submodule binds the Mediator leg/tail domain via the Med13 subunit, and this submodule-Mediator association precludes pol II recruitment. Collectively, these results reveal the CDK8 subcomplex functions as a simple switch that controls the Mediator-pol II interaction to help regulate transcription initiation and reinitiation events. As Mediator is generally required for expression of protein-coding genes, this may reflect a common mechanism by which activated transcription is shut down in human cells.
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Knuesel
authors.forename: Krista D
authors.initials: KD
authors.lastname: Meyer
authors.forename: Carrie
authors.initials: C
authors.lastname: Bernecky
authors.forename: Dylan J
authors.initials: DJ
authors.lastname: Taatjes
mesh_terms: D002843:Chromatin / Q000378:metabolism; D056850:Cyclin-Dependent Kinase 8; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism*; D004257:DNA Polymerase II / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D056892:Mediator Complex; D011485:Protein Binding; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D002843:Chromatin; C460107:MED12 protein, human; C488666:MED13 protein, human; D056892:Mediator Complex; D011994:Recombinant Proteins; D014157:Transcription Factors; C095686:CDK8 protein, human; D056850:Cyclin-Dependent Kinase 8; D018844:Cyclin-Dependent Kinases; D004257:DNA Polymerase II