Fig. 3. Bub1-RNAi cells arrest in mitosis when the spindle is destroyed. DLD-1 cells expressing a GFP-histone fusion protein were transfected with siRNA duplexes against lamin B1 (yellow), Bub1 (green) and BubR1 (red), and then analyzed by time-lapse microscopy either in the absence of drugs, or in the presence of nocodazole or nocodazole plus ZM447439. The time from NEB to anaphase onset was then determined or, in the presence of nocodazole, the time from NEB to mitotic exit was measured. Note that each symbol on the scatter plot represents a single cell and the time is on a log scale. P1 and P2 are sub-populations; see Table 2 and text for more details. Importantly, in the presence of nocodazole, only 2 out of 32 Bub1-RNAi cells (6%) exited mitosis within 100 minutes. However, in the presence of nocodazole plus ZM447439, 12 out of 35 Bub1-RNAi cells (34%) exited mitosis within 100 minutes.