Myosin-V is a processive actin-based motor

Class-V myosins, one of 15 known classes of actin-based molecular motors, h ave been implicated in several forms of organelle transport(1-5), perhaps w orking 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 cycle s and coupled mechanical advances for each diffusional encounter with its t rack. This allows single motors to support movement of an organelle along i ts track Here we provide direct evidence that myosin-V is indeed a processi ve actin-based motor that can move in large steps approximating the 36-nm p seudo-repeat of the actin filament.