Analysis of the comet-shaped accumulation of +TIPs at microtubule ends. (A, left) TIRF microscopy images of comet-like accumulations of H2-GFP (added at 75 nM) at the ends of individual microtubules growing with the indicated velocities in the presence of 150 nM of unlabeled EB1. Bar, 5 μm. (A, right) Averaged fluorescence intensity profiles of H2-GFP comets at different tubulin concentrations (from 50 individual comets per tubulin concentration; dots) were fitted (lines) using Gaussian (to the left of the vertical broken line) and single exponential (to the right of the vertical broken line) functions. (A, inset) Microtubule growth velocities as a function of the used tubulin concentrations (error bars indicate SD). (B) Comet tail lengths of H2-GFP (top) and CLIP-170–GFP (middle) in the presence of unlabeled EB1, and of EB1-GFP alone (bottom) as a function of the microtubule growth speed. The comet tail lengths were obtained from the single exponential fits to the averaged intensity profiles. H2-GFP and CLIP-170–GFP were added at 75 nM, and EB1 and EB1-GFP at 150 nM. (C) Characteristic end-decoration times of the +TIPs as indicated corresponding to the comet tail lengths in B. The characteristic decoration time in the comet tail was obtained by dividing the comet tail length by the microtubule growth speed. Vertical error bars in B and C represent the standard error, and horizontal error bars represent the SD of the growth velocity.