Western blot of human T-47D cells showing specific immunolabeling of the ~34k Cdc2 phosphorylated at Tyr15 (Control, lane 1). Treatment with EGF (30 ng per ml for 30 min) caused dephosphorylation of the Tyr15 on cdc2 (Lane 2). The phosphospecificity of this labeling is also shown in the third and fourth lanes (lambda-phosphatase: lambda-Ptase). These blots are identical to the control except that they were incubated in lambda-Ptase (1200 units for 30 min) before being exposed to the Phospho-Cdc2 Y15. The immunolabeling is completely eliminated by treatment with lambda-Ptase.