Chapter 12
- Mammalian cdk8 and cyclin C, and their yeast counterparts, are part of an RNA polymerase II holoenzyme. In this capacity, they phosphorylate the CTD of the polymerase II largest subunit. In mammals, cdk8 and cyclin C are also part of mediator complexes that repress transcription, independently of its phosphorylation of the polymerase CTD. Akoulitchev et al. show that these two proteins, in the context of the repressive mediators, exert repression by phosphorylating TFIIH. This blocks the CTD-phosphorylating activity, and also the transcription-activating activity, of TFIIH. (Akoulitchev, S., S. Chulkov, and D. Reinberg. 2000. TFIIH is negatively regulated by cdk8-containing mediator complexes. Nature 407:102-06)
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