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. Involved in regulation of membrane traffic between the Golgi and the endoplasmic reticulum (ER); the function is proposed to depend on its association in the interphase NRZ complex which is believed to play a role in SNARE assembly at the ER (By similarity). Interacts with NBAS and KNTC1/ROD; the interactions are mutually exclusive and indicative for its association in two different vesicle tethering complexes (By similarity). Component of the RZZ complex composed of KNTC1/ROD, ZW10 and ZWILCH (By similarity). Component of the NRZ complex composed of NBAS, ZW10 and RINT1/TIP20L; NRZ associates with SNAREs STX18, USE1L, BNIP1/SEC20L and SEC22B (the assembly has been described as syntaxin 18 complex) (By similarity). Interacts directly with RINT1/TIP20L bound to BNIP1/SEC20L (By similarity). Interacts with C19orf25 and ZWINT (By similarity). Interacts with ZFYVE1 (By similarity). Interacts with RAB18 and this interaction is enhanced in the presence of ZFYVE1 (By similarity). Dynamic pattern of localization during the cell cycle. In most cells at interphase, present diffusely in the cytoplasm. In prometaphase, associated with the kinetochore. At metaphase, detected both at the kinetochores and, most prominently, at the spindle, particularly at the spindle poles. In very early anaphase, detected on segregating kinetochores. In late anaphase and telophase, accumulates at the spindle midzone. Belongs to the ZW10 family.