Microtubule stability determines the duration of spindle movement. (A) Representative images of pre-anaphase cells with GFP-Tub1–labeled microtubules of the indicated genotypes. Each image is a maximum intensity projection from a confocal Z series. Bars, 1 µm. The corresponding kymographs track the fluorescence intensity of the spindle over time (10 min) showing spindle movement. (B) Mean of the maximum astral microtubule length reached during a sliding event in pre-anaphase cells. EpoA are WT cells treated with epothilone A. DMSO are WT cells treated with DMSO control. WT, n = 51 microtubules; tub2-430Δ, n = 97; kip3Δ, n = 208; EpoA, n = 106; DMSO, n = 42. (C) Mean sliding duration in seconds. WT, n = 52 microtubules; tub2-430Δ, n = 97; kip3Δ, n = 204; EpoA, n = 157; DMSO, n = 88. (D) Mean sliding frequency displayed in events per minute. WT, n = 91 microtubules; tub2-430Δ, n = 73; kip3Δ, n = 53; EpoA, n = 157; DMSO, n = 88. (E) Mean frequency of microtubule-cortex interactions per minute. WT, n = 39 cells; tub2-430Δ, n = 38; kip3Δ, n = 58. (B–E) Error bars are SEM. Asterisks denote a significant difference from WT. ***, P < 0.0006; ****, P < 0.0001; determined by t test. (F) Position of pre-anaphase spindles (<1.9 µm) in asynchronous cells. WT, n = 837 cells; dyn1Δ, n = 433; tub2-430Δ, n = 770; kip3Δ, n = 959. (G) Position of anaphase spindles (≥1.9 µm) in asynchronous cells. WT, n = 333 cells; dyn1Δ, n = 405; tub2-430Δ, n = 300; kip3Δ, n = 427. (F and G) Error bars are standard error of proportion.