FIG. 4.

Chemical stability of phosphorylated YPD1 and SSK1-R2. Phosphorylation reactions (30 μl) were carried out as described in the legend to Fig. 3 and stopped by the addition of stop buffer. The sample was divided into four aliquots, which were either left untreated (lane 1) or incubated for 10 min at 37°C alone (lane 2) or after the addition of HCl to a final concentration of 0.5 M (lane 3) or NaOH to a final concentration of 1 M (lane 4). Reaction products were separated on an SDS–15% polyacrylamide gel and analyzed by autoradiography.