Organizational Principles of the NuMA-Dynein Interaction Interface and Implications for Mitotic Spindle Functions.

Mitotic progression is orchestrated by the microtubule-based motor dynein, which sustains all mitotic spindle functions. During cell division, cytoplasmic dynein acts with the high-molecular-weight complex dynactin and nuclear mitotic apparatus (NuMA) to organize and position the spindle. Here, we analyze the interaction interface between NuMA and the light intermediate chain (LIC) of eukaryotic dynein. Structural studies show that NuMA contains a hook domain contacting directly LIC1 and LIC2 chains through a conserved hydrophobic patch shared among other Hook adaptors. In addition, we identify a LIC-binding motif within the coiled-coil region of NuMA that is homologous to CC1-boxes. Analysis of mitotic cells revealed that both LIC-binding sites of NuMA are essential for correct spindle placement and cell division. Collectively, our evidence depicts NuMA as the dynein-activating adaptor acting in the mitotic processes of spindle organization and positioning.