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Molecular and Cellular Biology, February 2009, p. 650-661, Vol. 29, No. 3
0270-7306/09/$08.00+0     doi:10.1128/MCB.00993-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The Human CDK8 Subcomplex Is a Histone Kinase That Requires Med12 for Activity and Can Function Independently of Mediator{triangledown}

Matthew T. Knuesel,1 Krista D. Meyer,1 Aaron J. Donner,2 Joaquin M. Espinosa,2 and Dylan J. Taatjes1*

Department of Chemistry and Biochemistry,1 Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 803092

Received 23 June 2008/ Returned for modification 17 July 2008/ Accepted 17 November 2008

The four proteins CDK8, cyclin C, Med12, and Med13 can associate with Mediator and are presumed to form a stable "CDK8 subcomplex" in cells. We describe here the isolation and enzymatic activity of the 600-kDa CDK8 subcomplex purified directly from human cells and also via recombinant expression in insect cells. Biochemical analysis of the recombinant CDK8 subcomplex identifies predicted (TFIIH and RNA polymerase II C-terminal domain [Pol II CTD]) and novel (histone H3, Med13, and CDK8 itself) substrates for the CDK8 kinase. Notably, these novel substrates appear to be metazoan-specific. Such diverse targets imply strict regulation of CDK8 kinase activity. Along these lines, we observe that Mediator itself enables CDK8 kinase activity on chromatin, and we identify Med12—but not Med13—to be essential for activating the CDK8 kinase. Moreover, mass spectrometry analysis of the endogenous CDK8 subcomplex reveals several associated factors, including GCN1L1 and the TRiC chaperonin, that may help control its biological function. In support of this, electron microscopy analysis suggests TRiC sequesters the CDK8 subcomplex and kinase assays reveal the endogenous CDK8 subcomplex—unlike the recombinant submodule—is unable to phosphorylate the Pol II CTD.

* Corresponding author. Mailing address: Department of Chemistry and Biochemistry, University of Colorado, Campus Box 215, Boulder, CO 80309. Phone: (303) 492-6269. Fax: (303) 492-5894. E-mail: taatjes{at}colorado.edu

{triangledown} Published ahead of print on 1 December 2008.

Molecular and Cellular Biology, February 2009, p. 650-661, Vol. 29, No. 3
0270-7306/09/$08.00+0     doi:10.1128/MCB.00993-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Firestein, R., Hahn, W. C. (2009). Revving the Throttle on an Oncogene: CDK8 Takes the Driver Seat. Cancer Res. 69: 7899-7901 [Abstract] [Full Text]  
  • Beckerman, R., Donner, A. J., Mattia, M., Peart, M. J., Manley, J. L., Espinosa, J. M., Prives, C. (2009). A role for Chk1 in blocking transcriptional elongation of p21 RNA during the S-phase checkpoint. Genes Dev. 23: 1364-1377 [Abstract] [Full Text]  
  • Knuesel, M. T., Meyer, K. D., Bernecky, C., Taatjes, D. J. (2009). The human CDK8 subcomplex is a molecular switch that controls Mediator coactivator function. Genes Dev. 23: 439-451 [Abstract] [Full Text]  


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