Tension is regulated by spindle structure. (A) Spindle and kMT lengths were measured in cells labeled with Spc110-mCherry and Nuf2-GFP. Bars, 1 μm. (B and C) Spindle length (B) and kMT length (C) in top2-4 and WT cells. (D) Tension regulation in top2-4 is accomplished via shorter kMT lengths and longer spindle lengths. (E) Experimental method to test whether dynamic kMTs are required to regulate tension in top2-4 cells. (F) In untreated cells, WT tension is maintained regardless of pericentromere stiffness (blue), but in cells treated with low-dose benomyl, which stabilizes kMTs, tension is reduced in top2-4 (red; control: n = 140 [WT] and n = 257 [top2-4]; benomyl: n = 215 [WT] and n = 197 [top2-4]). Horizontal lines and arrows are arithmetic means. (G) In benomyl, the relative difference in spindle length between WT and top2-4 is similar to untreated cells (vs. B). (H) In contrast, kMTs after benomyl treatment are longer in top2-4 (vs. C). (I) Tension regulation in top2-4 is disrupted when kMTs are stabilized in benomyl. Error bars = SEMs.