Figure 4.
Two-Step Model of Microtubule Maturation
(A) Kinetic model as in Figure 3A, but with an additional immature nonbinding state, A, that transforms at a rate k1 into an EB1 binding site, B.
(B) A global fit (black lines) to the three superaveraged EB1-GFP profiles from Figure 2C (green data points) using the two-step maturation model with binding kinetics. Fitting parameters are summarized in Table S1. Inset: two examples of time-averaged EB1 signals at constant EB1 concentration and different microtubule growth rates. Error bars are SE.
(C) Probability distributions of the EB1 binding site as calculated from the fits shown in (B).
(D) Peak positions of the probability distributions at different growth velocities. Filled black circles and open circles relate to (C) and Figure 6A, respectively.
(E) Theoretical number of tubulin dimers in maturation states A and B (bound and unbound to EB1), calculated from rate constants obtained from the fits in (B).
See also Figure S4.