Kip3 mediates a transition from dynamic to nondynamic spindle midzone when anaphase spindles reach the appropriate length. (a) FRAP analysis of spindle midzone microtubules before (elongating) or after (full length) anaphase spindles reached a length equal to cell length. Spindle midzones in cdc15-2 control cells (rows 1–2) or cells lacking Kip3 (rows 3–4) were photobleached during incubation at 37°C and fluorescence recovery was monitored over time. (b) Normalized midzone fluorescence recovery for representative spindles in the cell types corresponding to the rows in panel a. The average midzone fluorescence recovery rate ± SE for each cell type is plotted in panel c. P < 0.05 for full-length control versus elongating control, and for full-length control versus full-length kip3Δ spindles. For control n = 9 and 13, and for kip3Δ n = 10 and 9 for elongating and full-length spindles, respectively. Bar, 2 µm. See also Videos 1–4.