Stable cell lines expressing WT (A) or S628A/S629A mutant forms of FLAG-MCAK (B) were induced to express the ectoptic proteins and synchronized by an overnight thymidine block, reversal, and addition of nocodazole. When the majority of cells reached mitosis, the mitotic cells were shaken off, the nocodazole was removed, and mitotic progression was monitored microscopically after staining with a membrane permeable DNA binding dye. The percentage of the total cells at each of the indicated stages of mitosis are plotted for WT (A) and the S628A/S629A mutant (B) as a function of time.