Figure 9.
Inhibition of malE-mos- but not OA-induced MAP kinase activation allows cyclin B proteolysis. The electrophoretic mobility shift of MAP kinase caused by activating phosphorylation and the stability of 35S-labeled cyclin B were examined in extracts that were induced to enter mitosis by addition of Δ90 cyclin. The extracts contained either 20 μg/ml malE-mos or 1 μM OA and either 400 μM PD98059 or buffer. Samples were taken at the indicated time points and analyzed by SDS-PAGE and immunoblotting with Erk2 antibodies (anti-MAP kinase) or phosphorimaging (Cyc B). The positions of the slower-migrating bands representing active MAP kinase are indicated by arrowheads. Note that an activated form of MAP kinase cannot be detected in extracts treated with OA and PD98059.