Cyclin E kinase activity is decreased in CD44-ligated NB4 cells. (A) NB4 cells were lysed 0 hours and 48 hours after addition of A3D8 or IgG1 (controls). Cyclin E immunoprecipitates were analyzed by Western blotting with specific Abs to cyclin E, Cdk2, and p27. Relative protein levels were evaluated as described in Figure 2A and shown in italics below the lanes. Results represent 1 representative experiment of 3. (B) Cyclin E immunoprecipitates were incubated with histone H1 and [γ³²P]ATP (5000 Ci [1.85 × 10⁴ Bq]/mmol; ICN). γ³²P incorporation was measured as described in “Materials and methods.” The reaction products were separated by SDS-PAGE, proteins were transferred to nitrocellulose, and phosphorylated proteins were visualized by autoradiography. Phosphorylation was measured relative to controls. Results represent 1 representative experiment of 2.