Tau phosphorylation by GSK-3B. A) SDS-PAGE analysis of tau protein incubated for 20 h in the absence (lanes 1, 4, 7, 10, and 13) or the presence of 0.006 U GSK-3β per pmol tau (lanes 2, 5, 8, 11, 14) or 0.018 U GSK-3β per pmol tau (lanes 3, 6, 9, 12, and 15). A definite band shift in the migration of phosphorylated tau can be detected with increasing time and kinase concentration. B) The amount of γ-32P incorporation over time using 0.018 U GSK-3β per pmol tau (open circles, right y-axis) is compared to the SDS-PAGE analysis in Panel A (open squares, left y-axis). Lines are drawn through the points to ease comparison. Data represents a single trial.