Myosin-V is a processive actin-based motor

Class-V myosins, one of 15 known classes of actin-based molecular motors, have been implicated in several forms of organelle transport(1-5), perhaps working with microtubule-based motors such as kinesin(2-4,6). Such movements may require a motor with mechanochemical properties distinct from those of myosin-II, which operates in large ensembles to drive high-speed motility as in muscle contraction(7). Based on its function and biochemistry, it has been suggested that myosin-V may be a processive motor(7,8) like kinesing(9,10). Processivity means that the motor undergoes multiple catalytic cycles and coupled mechanical advances for each diffusional encounter with its track. This allows single motors to support movement of an organelle along its track Here we provide direct evidence that myosin-V is indeed a processive actin-based motor that can move in large steps approximating the 36-nm pseudo-repeat of the actin filament.