DIRECTION OF MICROTUBULE MOVEMENT IS AN INTRINSIC PROPERTY OF THE MOTOR DOMAINS OF KINESIN HEAVY-CHAIN AND DROSOPHILA NCD PROTEIN

The kinesin heavy chain and the ncd (non-claret disjunctional) gene product of Drosophila are microtubule-associated motor proteins related by sequence similarity within an almost-equal-to 340-aa domain. Despite the sequence similarity, the kinesin heavy chain and ncd protein move in opposite directions on microtubules. To investigate the molecular basis for direction of movement, we created a series of truncated kinesin heavy chain and ncd proteins. We found that the conserved domain of both proteins has microtubule motor activity, although the efficiency with which ATP hydrolysis is coupled to microtubule movement declines dramatically with increasing truncation. Further, the direction of movement is intrinsic to the conserved motor domains, rather than being a consequence of domain organization or adjacent sequences.