Effectiveness of wild-type (WT) Wee1A, T104A-Wee1A, T150A-Wee1A, and OP11-Wee1A at inhibiting mitotic entry. Interphase extracts were supplemented with 40 nM Wee1A and various concentrations of nondegradable Δ90-cyclin B. Extracts were incubated for 120 min, and then aliquots were taken for H1 kinase assays (A and B, top) and phospho-MAPK blot assays (B, bottom).