FIG. 4.

Activities of CDK complexes are higher in E6-expressing cells than control cells. Cyclin D/CDK4 or cyclin D/CDK6 (A) and cyclin A/CDK2 (B) complexes were immunoprecipitated, and kinase activities were determined as described in Materials and Methods. Autoradiographs of the CDK reactions are shown in the upper panels. The intensities of the bands were determined by Phosphorimager scanning (ImageQuant software; Molecular Dynamics). The glutathione S-transferase (GST)-pRb-kinase activities and the histone H1-kinase activities in E6-expressing cells were normalized to the activities in control cells. The data shown in panel B are the averages of the results of two independent experiments.