Walking on two heads: the many talents of kinesin.

The gallop of a race horse and the minute excursions of a cellular vesicle have one thing in common: they are based on the directional movement of proteins termed molecular motors -- many trillions in the case of the horse, just a few in the case of the cell vesicle. These tiny machines take nanometre steps on a millisecond timescale to drive all biological movements. Over the past 15 years new biochemical and biophysical approaches have allowed us to take a giant step forward in understanding the molecular basis of motor mechanics.