Schematic depicting Eg5 activity in the mitotic spindle. Tetrameric Eg5 motors (red) help organize microtubules (green) to form the mitotic spindle. (A) At the onset of mitosis, the duplicated centrosomes (blue) separate and nucleate two microtubule asters. Processive Eg5 motors may translocate to the plus-ends of microtubules, located distal to the centrosomal organizing center and by crosslinking antiparallel microtubules, may promote bipolarity. (B) By metaphase, a stable bipolar spindle has formed. Eg5 motors likely provide structural integrity and also slide microtubules toward the centrosomes, contributing to the generation of poleward flux. (C) A close-up depiction of Eg5 motors walking to the plus ends of antiparallel microtubules, moving both poleward simultaneously.