Important role in mitotic dividing cells (PubMed:8227131). Microtubule motor required for spindle body separation (PubMed:8918872). Slow plus-end directed microtubule motor capable of cross-linking and sliding apart antiparallel microtubules, thereby pushing apart the associated spindle poles during spindle assembly and function (PubMed:8918872, PubMed:8589456, PubMed:19062285). Forms cross-links between microtubules within interpolar microtubule bundles (PubMed:9885249, PubMed:19158379). Contributes to the length of the metaphase spindle, maintains the prometaphase spindle by antagonizing Ncd, drives anaphase B, and also contributes to normal chromosome congression, kinetochore spacing, and anaphase A rates (PubMed:19158379). Displays microtubule-stimulated ATPase activity (PubMed:8589456). Required for normal fusome organization (PubMed:10469596). Required in non-mitotic cells for transport of secretory proteins from the Golgi complex to the cell surface (PubMed:23857769). Homotetramer (PubMed:8538794, PubMed:9885249, PubMed:24714498). Consists of two pairs of polypeptides associated by coiled-coil interactions to form two homodimers (PubMed:8538794). The homodimers are linked by lateral interactions between their coiled-coil regions to form a bipolar homotetramer consisting of a central rod with two motor domains projecting from either end (PubMed:8538794). Parallel coiled coils extend from each pair of motor heads, switch to two antiparallel coiled coils in the central region and then back to parallel coiled coils (PubMed:24714498). Interacts with Wee1 (PubMed:19800237). In somatic cells, cytoplasmic during interphase, localized to centrosomal asters at the onset of mitosis in prophase and associated with spindle structures during the remainder of mitosis (PubMed:10469596). In male and female germ cells, associates with fusomes during interphase, then localizes to centrosomal asters during prophase and to spindles in metaphase (PubMed:10469596). Coincident with spindle microtubules from prophase to metaphase and, as mitosis proceeds, found both at the spindle poles and along the spindle fibers (PubMed:8589456). Specifically expressed in proliferating tissues during embryonic and larval development. Phosphorylation is required for localization to mitotic spindles (PubMed:9885249). Phosphorylation of Thr-933 during mitosis controls association with the spindle apparatus (By similarity). Phosphorylated in vitro by Wee1 (PubMed:19800237). Belongs to the TRAFAC class myosin-kinesin ATPase superfamily. Kinesin family. BimC subfamily.