REVERSAL IN THE DIRECTION OF MOVEMENT OF A MOLECULAR MOTOR

Kinesin and non-claret disjunctional (ncd) are molecular motors of the kinesin superfamily that move in opposite directions along microtubul es. The molecular basis underlying the direction of movement is unclea r, although it is thought to be an intrinsic property of the motor dom ain, a conserved region about 330 amino acids in length(1-3). The moto r domain is found at the amino terminus in conventional kinesins, but at the carboxy terminus in ncd(4,5). Here we report on a chimaera comp osed of the motor domain of the minus-end-directed kinesin of Neurospo ra crassa(6). The bacterially expressed fusion protein was tested in m otility assays using polarity-marked microtubules(7). Surprisingly, th e chimaera moved towards the plus end, demonstrating that the polarity of force generation of the ncd motor domain has been reversed. This f inding indicates that the domain organization, particularly the positi on of the motor domain, is of fundamental importance for the polarity of force production. It also demonstrates that the direction of microt ubule movement is not controlled solely by the motor domain(8).