Fig. 3. Chromosome missegregation in ekc1 and Δppe1 mutants in the presence of TBZ. (A) Moderate hypersensitivity of ekc1-163, Δppe1, mis12, ekc1-163 mis12 and Δppe1 mis12 mutants to TBZ, a microtubule-destabilizing drug. Exponentially growing cells were diluted and spotted onto YPD plates that contained 20 µg/ml TBZ, and incubated at 33°C. nda2-KM52, an α-tubulin mutant, was used as a control hypersensitive mutant. (B) Unequal chromosome segregation frequently occurred in ekc1-163, Δppe1, ekc1 mis12 and Δppe1 mis12 mutant cells in the presence of TBZ. Wild-type and mutant cells were cultured at 33°C, and TBZ (20 µg/ml) was added (time 0). The frequency of dividing cells did not change after TBZ addition, whereas the frequency of mutant cells displaying unequal nuclear division increased to 48–55% (of binucleate cells) after 4 h. (C) Mis-segregation of sister chromatids in ekc1-163 and Δppe1 was confirmed through the use of cen1[lys1]–GFP, a cen1-proximal DNA marker (arrowheads) (33°C, 4 h after TBZ addition). Bar, 10 µm.