t(8;21) cell lines have disrupted spindle checkpoint. (A) Immunoblot of lysates from K562, Kasumi-1, and SKNO-1 cells treated without (−) or with (+) 1 μg/mL nocodazole for 18 hours. Membranes were probed with antibodies for BubR1, Bub3, separase, cohesin subunit Rad21/scc1, and securin. Tubulin immunoblot shows relative protein loading. (B) Kasumi-1, SKNO-1, and K562 cells were treated with nocodazole for 18 hours and labeled with 10 μM BrdU for 24 hours. Cells were fixed and stained with anti–BrdU-FITC and analyzed by flow cytometry. The percentage of cells stained positive for BrdU is shown.