Essential for yeast nuclear fusion during mating. KAR3 is a bifunctional protein having a kinesin-like motor domain joined to a distinct microtubule binding domain. It may mediate microtubule sliding during nuclear fusion and possibly mitosis. May interact with spindle microtubules to produce an inwardly directed force acting upon the poles. KAR3 function antagonizes CIP8 and KIP1 outward force action. KAR3 motor activity is directed toward the microtubule's minus end. Interacts with CIK1 and VIK1. Cytoplasmic microtubules. By alpha factor. KAR3 contains two globular domains separated by an alpha-helical coiled coil. The N-terminal portion of KAR3 contains a microtubule association domain distinct from the kinesin-like C-terminal domain. Present with 3250 molecules/cell in log phase SD medium. Belongs to the TRAFAC class myosin-kinesin ATPase superfamily. Kinesin family. NCD subfamily.