Inhibition of transcription by the trimeric cyclin-dependent kinase 7 complex

Cyclin-dependent kinase 7 (CDK7) can be isolated as a subunit of a trimeric kinase complex functional in activation of the mitotic promoting factor. I n this study, we demonstrate that the trimeric cdk-activating kinase (CAK) acts as a transcriptional repressor of class II promoters and show that rep ression results from CAK impeding the entry of RNA polymerase II and basal transcription factor IIF into a competent preinitiation complex. This repre ssion is independent of CDK7 kinase activity. We find that the p36/mAT1 sub unit of CAK, is required for transcriptional repression and the repression is independent of the promoter used. Our results demonstrate a central role for CAK in regulation of messenger RNA synthesis by either inhibition of R NA polymerase II-catalyzed transcription or stimulation of transcription th rough association with basal transcription repair factor IIH.