Essential component of the mitotic checkpoint, which prevents cells from prematurely exiting mitosis (PubMed:18765790). Required for chromosome segregation, the assembly of the dynein-dynactin and mdf-1-mdf-2 complexes onto kinetochores and spindle pole separation (PubMed:18765790). Its function related to the spindle assembly machinery and kinetochore-microtubule attachments likely depends on its association in the mitotic RZZ complex (PubMed:18765790). The RZZ complex recruits the spindly-like protein spdl-1 to kinetochores (PubMed:18765790). To prevent irregular chromosome segregation, the complex also inhibits the attachment of the kinetochore-associated NDC80 complex to microtubules (PubMed:24231804). The recruitment of spdl-1 to kinetochores relieves this inhibition (PubMed:24231804). Required for embryonic development (PubMed:18765790, PubMed:19109417). Component of the RZZ complex composed of rod-1, czw-1 and zwl-1 (PubMed:18765790). Interacts with the spindly-like protein spdl-1 (PubMed:18765790). Interacts with NDC80 complex component ndc-80 (PubMed:24231804). Localizes to the kinetochore during nuclear envelope breakdown and remains there until the metaphase-anaphase transition (PubMed:18765790). Localizes to kinetochores, spindle-associated rod-shaped structures and near the cell cortex in a knl-1-dependent manner in anaphase (PubMed:18765790, PubMed:20729837). RNAi-mediated knockdown results in embryonic lethality (PubMed:18765790, PubMed:19109417). RNAi-mediated knockdown results in defective chromosome segregation, premature spindle pole separation and incorrectly attached kinetochores (PubMed:18765790). In addition, knl-1 localization to the spindle-associated rod-shaped structures but not to kinetochores is lost during anaphase of meiosis I (PubMed:20729837). RNAi-mediated knockdown also results in abolished targeting of the spindly-like protein spdl-1 to the kinetochore (PubMed:18765790). Belongs to the ZWILCH family.