MOTORING DOWN THE HIGHWAYS OF THE CELL

All eukaryotic cells contain large numbers of motor proteins (kinesins , dyneins and myosins), each of which appears to carry out a specializ ed force-generating function within the cell. They are known to have r oles in muscle contraction, ciliary movement, organelle and vesicle tr ansport, mitosis and cytokinesis. These motor proteins operate on diff erent cytoskeletal filaments; myosins move along actin filaments, and kinesins and dyneins along microtubules. Recently published crystal st ructures of the motor domains of two members of the kinesin superfamil y reveal that they share the same overall fold that is also found at t he core of the larger myosin motor. This suggests that they may share a common mechanism as well as a common ancestry.