A subset of MDA-MB-468 cells arrest in late G₂ following nocodazole or vincristine treatment. Cells growing on coverslips were treated with diluent (a and d), 1 μM nocodazole (b and e), or 100 nM vincristine (c and f) for 24 hours, then fixed and stained with antibodies to CENP-F (a–c) or cyclin B (d–f). (g) The percentage of cells displaying focal nuclear CENP-F localization (arrow in a) increased after a 24-hour treatment with nocodazole or vincristine. Results shown are mean ± SD of three separate experiments. Ionizing radiation was used as a positive control. Quantitative analysis demonstrated that the number of cells with cytoplasmic cyclin B localization increased in a very similar fashion.