CCNH is part of the cyclin family that is known for its protein abundance through the cell cycle. Cyclins act as regulators of CDK kinases. CCNH forms a complex with CDK7 kinase and ring finger protein MAT1. The kinase complex is able to phosphorylate CDK2 and CDC2 kinases, therefore it functions as a CDK-activating kinase (CAK). CCNH and its kinase collaborator are components of TFIIH, as well as RNA polymerase II protein complexes Synonyms: CCNH, CAK, p34, p37, Cyclin-H, MO15-associated protein