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Journal Article

Structure of the mediator subunit cyclin C and its implications for CDK8 function.


Cramer,  P.
Department of Molecular Biology, MPI for Biophysical Chemistry, Max Planck Society;

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Hoeppner, S., Baumli, S., & Cramer, P. (2005). Structure of the mediator subunit cyclin C and its implications for CDK8 function. Journal of Molecular Biology, 350(5), 833-842. doi:10.1016/j.jmb.2005.05.041.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0015-847A-6
Cyclin C binds the cyclin-dependent kinases CDK8 and CDK3, which regulate mRNA transcription and the cell cycle, respectively. The crystal structure of cyclin C reveals two canonical five-helix repeats and a specific N-terminal helix. In contrast to other cyclins, the N-terminal helix is short, mobile, and in an exposed position that allows for interactions with proteins other than the CDKs. A model of the CDK8/cyclin C pair reveals two regions in the interface with apparently distinct roles. A conserved region explains promiscuous binding of cyclin C to CDK8 and CDK3, and a non-conserved region may be responsible for discrimination of CDK8 against other CDKs involved in transcription. A conserved and cyclin C-specific surface groove may recruit substrates near the CDK8 active site. Activation of CDKs generally involves phosphorylation of a loop at a threonine residue. In CDK8, this loop is longer and the threonine is absent, suggesting an alternative mechanism of activation that we discuss based on a CDK8–cyclin C model.