Fig. 2.

Measurements of microtubule trajectories. (a) Microtubule trajectories under an electric field E = 18 kV/m. All trajectories acquired during a 15-min measurement are shown. The dashed line shows the average trajectory that we infer from analysis of the curvature (Eq. 11 in SI Text). (b) Selection of trajectories at two different field strengths. At the highest electric field (red) the curvature is clearly more pronounced and the alignment is faster. (c) Overlapping coordinates of leading (red triangles) and trailing (green circles) ends of two different microtubules under different electric fields show that there is no motion perpendicular to the microtubule axis. The orientation θ′_m of the leading tip of the microtubule, just before attachment to the next kinesin motor, determines the trajectory curvature $\frac{d\theta }{ds}$ at any point s along the trajectory.