Figure 2.

OA inhibits cyclin B proteolysis if added before entry into mitosis. H1 kinase activity, the phosphorylation-induced mobility shift of ³⁵S-labeled Cdc25 and of Cdc27, and the degradation of ³⁵S-labeled cyclin B (Cyc B) were analyzed in extracts treated either with buffer (A) or with 1 μM OA (B and C), which was added either at time zero (B) or 25 min later (C). Δ90 was added to all reactions at time zero. Samples were taken at the indicated time points and analyzed by kinase assays and by SDS-PAGE followed by immunoblotting (anti-Cdc27) or phosphorimaging (H1 kinase, Cdc25, and Cyc B). The time points of buffer and OA addition are marked by arrows.