Essential component of the mitotic checkpoint, which prevents cells from prematurely exiting mitosis (PubMed:15886105, PubMed:17576797). Required for the assembly of the dynein-dynactin, Mad2 complexes and spindly/CG15415 onto kinetochores (PubMed:15886105, PubMed:17576797). Its function related to the spindle assembly machinery is proposed to depend on its association in the RZZ complex (PubMed:22685323). Failure to assemble the complex due to the absence of any one of its components, results in the incorrect redistribution of the remaining components to diverse membrane compartments (PubMed:22685323). Component of the RZZ complex composed of rod, Zw10 and Zwilch. Dynamic pattern of localization during the cell cycle (PubMed:22685323). In most cells at interphase, present diffusely in the cytoplasm (PubMed:22685323). At metaphase, detected at the kinetochores and kinetochore microtubules, and in late anaphase and telophase accumulates at the spindle envelope midzone (PubMed:12686595, PubMed:22685323). Lagging chromosomes at anaphase and precocious sister chromatid separation upon activation of the spindle checkpoint (PubMed:12686595). In spermatocytes the number of Golgi structures are not affected but they show a mild defect in shape (PubMed:22685323). Belongs to the ZWILCH family.