Western blot of human T47D cells showing specific immunolabeling of the ~45k MEK 1 (Control). The phosphospecificity of this labeling is shown in the second lane (lambda phosphatase: I>> Ptase) The blot is identical to the control except that it was incubated in I>> Ptase (1200 units for 30 min) before being exposed to the MEK 1 Thr386 antibody. The immunolabeling of MEK 1 is completely eliminated by I>> Ptase.