CLASP1 promotes the depolymerization of GMPCPP-stabilized microtubules in a GTP-dependent manner. (A) Schematic of the microtubule depolymerization assay. (B) Representative kymographs of GMPCPP-stabilized microtubules incubated with storage buffer, 200 nM chTOG, or 200 nM CLASP1. (C) Representative kymographs of GMPCPP-stabilized microtubules incubated with storage buffer, 200 nM chTOG, or 200 nM CLASP1 in the presence of 1 mM GTP. (D) Quantification of microtubule depolymerization rates for the conditions in B and C. N = 50–108 microtubules for each condition across at least two experimental days. Individual data points from different experiments are plotted in different shades, and the means for each experimental repeat are plotted as larger points in the same color. The squares indicate the average of the experimental means, and the vertical bars are the standard errors of the means. See also Video 1. For comparison between the no GTP conditions, a one-way ANOVA followed by Tukey’s HSD test for multiple comparisons found that the mean rate of microtubule depolymerization was significantly different between the buffer control vs. chTOG (P < 0.001) and chTOG vs. CLASP1 (P < 0.001) in the absence of GTP. There was no statistically significant difference between the buffer control and CLASP1 condition (P = 0.06) in the absence of GTP. Welch’s two-tailed unequal variances t tests were performed for pairwise comparison of the no-GTP vs. GTP conditions and the corresponding P values are indicated on the graph.