Phosphorylation of p53 by GSK3β. p53-GST (2 μg) was incubated in the absence (Control) or presence of the indicated protein kinase as described in methods. Primary kinases were then heat inactivated (65°C/15 min). Aliquots of the phosphorylated p53-GST were then incubated in the absence (-), or presence of recombinant GSK3α (α) or GSK3β (β) and 10 μCi 32P-ATP. Phosphorylated p53-GST (0.25 μg total p53-GST was detected by SDS-PAGE followed by auto-radiography. MAPK, MAP kinase; S6 Kin, S6 Kinase; PKA, Protein Kinase A; PKC, Protein Kinase C.