Required for assembly of the mitotic spindle. Interacts with spindle microtubules to produce an outwardly directed force acting upon the poles. Following spindle assembly, CIN8 and KIP1 apparently act to oppose a force that draws separated poles back together. This force seems to be mediated by KAR3 (By similarity). Spindle microtubules that lie between the poles. Belongs to the TRAFAC class myosin-kinesin ATPase superfamily. Kinesin family. BimC subfamily.