Figure 5.

Activation of Cdc2 by exogenous cyclin BΔ90 triggers entry into M-phase in MEK(QP) interphase extracts. (A) MEK(QP) was added to cycling extracts, and then reactions were incubated at room temperature. At 40 min, samples were taken, then 1 min later a buffer or cyclin BΔ90 was added, and samples were taken during further incubation. Samples were analyzed by immunoblotting with anti-Cdc25 antibodies (top), anti-phosphotyrosine antibodies (middle), and anti-cyclin B2 antibodies (bottom). Bold line indicates time points when NEBD and CC were observed. (B) Samples from the experiment in A were immunoblotted with anti-p90rsk antibodies. Bold line indicates time points when NEBD and CC were observed. (C) Extracts were prepared from cycloheximide-treated activated eggs that lack mitotic cyclins (see MATERIALS AND METHODS), cyclin BΔ90 protein was added, and then samples were taken during further incubation and immunoblotted with anti-p90rsk antibodies. Bold line indicates time points when NEBD and CC were observed.