Kinetic analysis of SF3b1 phosphorylation by DYRK1A and CDK2. SF3b1-NT-His6 was phosphorylated with GST-DYRK1A-ΔC or cyclin E/CDK2 at two different substrate concentrations (0.7 and 7 μM). Phosphate incorporation was measured at different time points (2, 4 and 8 minutes). The slope of the straight line reflects the velocity of phosphorylation at the different substrate concentrations. The calculated K
values are indicated. The experiment was repeated with similar results.