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Figure S1. (A and B) Vanadate treatment increases the length of spindles. Spindles fixed 8 min after addition of control buffer (A), or 100 µM vanadate (B). Tubulin, red; DNA, blue. (C-H) Low concentration of p150-CC1 has the same effect on spindle assembly as a high concentration of p50 dynamitin. Control buffer (C and F), 18 µM p50 dynamitin (D and G), or 56 nM p150-CC1 (E and H) were added at the start of spindle assembly reactions. (C-E) Overlays of tubulin (red), DNA (blue). (F-H) Tubulin alone. (I-M) Spindle length regulation by dynactin is independent of pole focusing. (I-L) Spindles assembled in the presence of 18 µM p50 dynamitin (I and K), or 56 nM p150-CC1 (J and L), and treated with additional p150-CC1 (2 µM for 15 min) after assembly. (I and J) Overlays of tubulin (red), DNA (blue). (K and L) Tubulin alone. (M) Control buffer, 18 µM p50 dynamitin, or 56 nM p150-CC1 were added at the start of spindle assembly reactions. After assembly, p150-CC1 was added (2 µM), samples were fixed 0, 8, or 15 min later, and lengths were measured and normalized to the length of untreated spindles (40 µm) (mean ± SD, n =15, two independent experiments). Bars, 10 µm.