Western blot of rat brain nuclear fraction lysate showing specific immunolabeling of the ~53k p53 phosphorylated at Ser392 (Control). The phosphospecificity of this labeling is shown in the second lane (lambda-phosphatase: λ-Ptase). The blot is identical to the control except that it was incubated in λ-Ptase (1200 units for 30 min) before being exposed to the phospho Ser392 p53 antibody. The immunolabeling is completely eliminated by treatment with λ-Ptase.