Processive movement of single 22S dynein molecules occurs only at low ATP concentrations

We have analyzed the movement of single 22S dynein molecules from Tetrahymena cilia by using a nanometer measuring system equipped with optical tweezers. Statistical analysis proved that a single molecule of 22S dynein can move processively and develop force at low concentrations of ATP (<20 μM). The maximum force was ≈4.7 pN, and the force-velocity curve was convex down. During force development, dynein molecules showed stepwise displacement of ≈8 nm and frequently exhibited backward steps of ≈8 nm. At higher concentrations of ATP (≧20 μM) single molecules of 22S dynein were not observed to move processively. Twenty-two S dynein seems to switch over from a processive mode to a nonprocessive mode, sensing a subtle change of ATP concentrations. These observations indicate that the processivity, maximum force, and step size of dynein are similar to those of kinesin, but the ATP concentration-dependence, force-velocity relationship, and backward steps are clearly distinct from kinesin.