A HUMAN PRIMARY T-LYMPHOCYTE-DERIVED HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 TAT-ASSOCIATED KINASE PHOSPHORYLATES THE C-TERMINAL DOMAIN OF RNA-POLYMERASE-II AND INDUCES CAK ACTIVITY

Tat protein mediates transactivation of human immunodeficiency virus t ype 1 (HIV-1), which results in more-efficient transcript elongation, Since phosphorylation of C-terminal domain (C-ID) of RNA polymerase II correlates with its enhanced processivity, we studied the properties of a Tat-associated CTD kinase derived cd from mitogenically stimulate d human primary T lymphocytes (TTK). TTK binds to full-length Tat and specifically phosphorylates CTD and CDK2. This dual kinase activity is characteristic of CDK-activating kinase (CAK). The CTD kinase activit y is induced upon mitogenic stimulation of primary T lymphocytes. Frac tionation of T-cell lysate demonstrates that Tat-associated CTD kinase activity elutes in two peaks, About 60% of Tat-associated CTD kinase copurifies with CDK2 kinase activity and contains the CAK components C DK7 and cyclin H, The rest of Tat associated kinase is free of CDK2 ki nase activity and the CAK components and thus may represent a novel CT D kinase. The kinase activities of TTK are blocked by the adenosine an alog 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole (DRB) as well a s by the kinase inhibitor I-is at concentrations known to block transc ript elongation. Importantly, the Tat-associated kinase markedly induc ed CAK. We suggest that the mechanism of Tat-mediated processive trans cription of the HIV-1 promoter includes a Tat-associated CAK activator .