D. Plot of initial MT polymerization velocities at 37 °C in the presence of increasing concentrations of WT or NN. Tubulin concentration = 5 μM. Each point represents an average of 3 independent measurements of the rate of turbidity increase measured at 500 nm wavelength (OD500/min). Fitted are sigmoidal dose-response curves: Y = YB + ((YT - YB)/(1 + 10Xi - X)), where YB and YT are Y values (OD500/min) at the bottom and top plateaus, respectively, and Xi is the X value at the inflection point. Representative MT samples from 2:5 μM WT:tubulin or NN:tubulin incubations are shown in E and F, respectively. MT architecture distributions for WT and NN are shown with pie graphs. 