The core of the motor domain determines the direction of myosin movement

Myosins constitute a superfamily of at least 18 known classes of molecular motors that move along actin filaments(1-3). Myosins move towards the plus end of F-actin filaments; however, it was shown recently that a certain cla ss of myosin, class VI myosin, moves towards the opposite end of F-actin, t hat is, in the minus direction(4). As there is a large, unique insertion in the myosin VI head domain between the motor domain and the light-chain-bin ding domain (the lever arm), it was thought that this insertion alters the angle of the lever-arm switch movement, thereby changing the direction of m otility(4). Here we determine the direction of motility of chimaeric myosin s that comprise the motor domain and the lever-arm domain (containing an in sert) from myosins that have movement in the opposite direction. The result s show that the motor core domain, but neither the large insert nor the con verter domain, determines the direction of myosin motility.