CDK-activating kinase that modulates CDKD-2 and CDKD-3 activities by phosphorylation of the T-loop. Activates CDKD-2 C-terminal domain (CTD) kinase activity. Activates CDKA-1 probably by phosphorylation. Posseses a CDK kinase activity independently of association with cyclin CYCH1-1. Phosphorylates the CTD of the large subunit of RNA polymerase II.