Bub3 is required for correct chromosome segregation. (A) The duration of prometaphase at 30°C in bub3Δ, bub3Δ mad2Δ, mad2Δ and wild-type (wt) cells was determined by live-cell microscopy using Plo1–GFP as a marker. In all box-whisker graphs, the lines from top to bottom are: maximum value, 75th percentile, median, 25th percentile and minimum value. (B) Cells carrying cen2–GFP and mCherry–atb2(tubulin) were synchronized with HU, released from HU arrest and arrested in mitosis by treatment with the microtubule-destabilizing drug MBC for 3.5 h. After washout of MBC, segregation of chromosome 2 (cen2–GFP) was followed by live-cell microscopy at 20°C. Only those cells that were already in mitosis when recording was started were considered. Mis-segregation in unperturbed mitosis was similarly determined by live-cell microscopy at 20°C after HU release. GFP, green fluorescent protein; HU, hydroxyurea.