FIGURE 3.

Ibulocydine inhibits Cdk7 and Cdk9 activity in vitro. Kinase assays were performed at 30 °C for 20 min in the reaction buffer containing RNA polymerase II-CTD-GST recombinant protein as a specific substrate for each kinase. Recombinant Cdk7 and Cdk9 proteins were used as the enzyme source. Radioactivity trapped in SDS-PAGE gels was measured using a phosphorimage analyzer in two independent experiments. Bar graphs show relative percentage (mean values) of inhibition of kinase activity by ibulocydine (dark gray columns), BMK-Y101 (gray columns), or roscovitine (white columns). Error bars represent mean ± S.E. of two independent experiments.