THE DIRECTIONAL PREFERENCE OF KINESIN MOTORS IS SPECIFIED BY AN ELEMENT OUTSIDE OF THE MOTOR CATALYTIC DOMAIN

Members of the kinesin superfamily share a similar motor catalytic dom ain yet move either toward the plus end (e.g., conventional kinesin) o r the minus end (e.g., Ncd) of microtubules. The structural features t hat determine the polarity of movement have remained enigmatic. Here, we show that kinesin's catalytic domain (316 residues) in a dimeric co nstruct (560 residues) can be replaced with the catalytic domain of Nc d and that the resultant motor moves in the kinesin direction. We also demonstrate that this chimera does not move processively over many tu bulin subunits, which is similar to Ncd but differs from the highly pr ocessive motion of conventional kinesin. These findings reveal that th e catalytic domain contributes to motor processivity but does not cont rol the polarity of movement. We propose that a region adjacent to the catalytic domain serves as a mechanical transducer that determines di rectionality.