Fig. 3. Polo degradation is mediated by the proteasome. (A) Inhibition of the proteasome with lactacystin significantly slows down the rate of Polo degradation in geldanamycin-treated cells. (B) The kinase activity of Polo drops dramatically as early as 24 h after geldanamycin treatment, even when Polo degradation is retarded by lactacystin.