FIG. 3.

Kinetics of CREB bZIP dissociation in the presence of Tax and KIX. The 73-aa bZIP domain of CREB was incubated with the viral CRE probe in the absence or presence of Tax or of Tax plus KIX. Binding-reaction mixtures were then challenged with a 1,000-fold molar excess of unlabeled cellular CRE binding site, and the kinetics of dissociation were analyzed by EMSA and quantitated by ImageQuant. The concentration of protein-DNA complexes remaining bound, relative to the concentration bound at time zero (no added competitor) (B/B₀), was plotted as a function of the time after challenge. The dissociation of CREB bZIP from the viral CRE probe (solid squares) in the presence of Tax (open squares) or in the presence of Tax plus KIX (solid triangles) is shown.