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Updated: May 5, 2026

Assaying Protein Kinase Activity with Radiolabeled ATP
Published on: May 26, 2017
Alternative mechanisms of CAK assembly require an assembly factor or an activating kinase
R P Fisher1, P Jin, H M Chamberlin
1Department of Physiology, University of California, San Francisco 94143-0444, USA.
Abstract:
We have cloned a mouse cDNA that encodes p36, a novel subunit of the CDK-activating kinase (CAK). p36 contains a C3HC4 zinc-binding domain or RING factor and is associated both with a TFIIH-bound form of CAK and with a free trimeric form. p36 promotes the assembly of CDK7 and cyclin H in vitro, stabilizing the transient CDK7-cyclin H complex. Stabilization and activation of CAK by p36 is independent of the phosphorylation state of T170, the conserved activating residue of CDK7. Assembly of active CDK7-cyclin H dimers can also occur through an alternative p36-independent pathway that requires phosphorylation of T170 by a CAK-activating kinase, or CAKAK. Thus, CDK7-cyclin H complex formation can be achieved by multiple mechanisms.
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