FIGURE 4.

The effect of a prolyl isomerase on the activity of hCDK12. a, an autoradiogram of a SDS-PAGE gel from an hCDK12/CyclinK kinase assay with increasing amounts of the prolyl isomerase Ess1. Assays were performed using 1 μg of GST-yCTD as a substrate at 30 μm ATP, 37 °C, and 15/30 min reaction times. b, quantification of the degree of phosphorylation of each mutant substrate using a PhosphorImager and ImageQuant software (normalized to a value of 1.0 for the 0 μm Ess1). No stimulation of hCDK12 activity was observed.