Essential component of the mitotic checkpoint, which prevents cells from prematurely exiting mitosis. Required for the assembly of the dynein-dynactin and MAD1-MAD2 complexes onto kinetochores. Its function related to the spindle assembly machinery is proposed to depend on its association in the mitotic RZZ complex (By similarity). Component of the RZZ complex composed of KNTC1/ROD, ZW10 and ZWILCH; in the complex interacts directly with KNTC1/ROD (By similarity). Belongs to the ZWILCH family.