Figure 5.

CDK9 phosphorylates the AR on S81 in vitro. Kinase assays were performed using purified CDKs, AR, histone, and PDKtide. Equivalent specific activities of the kinases were used (see panel C). A, Phosphorylation was assessed using phospho-specific antibodies. The no kinase control is represented by (−). Phosphorylation of S81, 94, and 16 is shown. The far lane in each blot is the corresponding S/A mutant control for antibody specificity. B, Quantitation of phospho-S81 levels. *, P = 0.001 compared with no kinase (−) control.