Kinetochore stretching promotes APC/C activation in metaphase. (A) Metaphase to anaphase transition in control or in 7 ng/ml nocodazole-treated cells. Levels of mCherry–cyclin B1 were followed with Hoechst DNA staining. Images were extracted from long-term imaging experiments and aligned on the time axis according to the metaphase alignment. (B) Kinetics of cyclin B1 proteolysis. Fluorescence intensities of cyclin B1 were measured during metaphase cells from both mock-treated (black line; n = 12) and 7 ng/ml nocodazole-treated experiments (brown line; n = 12), and the mean ± SD was plotted for each time point. Levels of fluorescence were normalized to the value just after the metaphase alignment. Arrowheads indicate the time points when cyclin B1 begin to degrade. (C) Quantification of the cyclin B1 degradation rate. The degradation rate of cyclin B1 intensities from 12 cells were averaged for each experiment and are shown in a histogram with SEM. A.U., arbitrary unit. Bar, 10 µm.