Figure 3. Inefficient degradation of cyclin B1 in anaphase re-activates the spindle checkpoint right after sister chromatid disjunction. The fluorescence intensity in live U2OS cells expressing Δ52–85-cyclin B1-Cerulean was plotted against time from NEB; (A) cells that divided normally. The arrow indicates the start of sister separation. (B) cells that arrested in a post-metaphase state; (C) Bar graph of the fluorescence levels at start of sister separation of cells plotted in (A and B); (D) Comparison of the fluorescence levels at the start of sister chromatid separation as compared with 12 min after sister chromatid separation in cells that either divided (plotted in A) or arrested (plotted in B).