FIG. 5.

Cyclin T1, but not Cdk9 or cyclin T2, protein levels are increased upon PMA treatment of promonocytic cell lines. The promonocytic cell lines HL-60 and U937 were cultured in media containing 10% FBS (−) or with the addition of PMA (1 ng/ml) (+) for 48 h. Cell lysates were prepared, and equal amounts of protein were assayed for TAK activity by a kinase assay with recombinant CTD as a substrate (A) or for protein levels of Cdk9 or cyclin T1 (Cyc T1) by immunoblotting (B). CTDo, hyperphosphorylated form of the CTD; CTDa, underphosphorylated form of the CTD. (C) Cyclin T2 was detected by immunoprecipitation of Cdk9-containing complexes with an antibody directed against Cdk9 followed by immunoblotting with an antibody directed against cyclin T2. Recombinant cyclin T2a (Cyc T2a) and cyclin T2b (Cyc T2b) were used as standards.