Figure 4.

Representative tracking of MT and attached particle movements, measured from the video used in Figure 2 with corresponding time points. (A) Positions of two ends of the MT and of the attached particle are traced. Inset, frame-by-frame analysis of the time at which the particle reaches and leaves the trailing MT end. The 3-s measurement of length of stay (horizontal bar) is detected from the point at which the end of the MT is no longer separately discernable to the point where the end reappears (broken lines). (B) Velocities of the MT and particles calculated using a moving average of three successive measurements of position. The differences between measurements of moving leading and trailing MT ends indicate the measurement error, exaggerated by the moving average. Note that the particle is constantly moving at slightly slower velocity than the MT. The rapid drop off of particle velocity beginning at 20 s reflects the time at which the particle leaves the MT end.