Essential component of the mitotic checkpoint, which prevents cells from prematurely exiting mitosis (PubMed:9298984). Required for the assembly of the dynein-dynactin and mdf-1-mdf-2 complexes onto kinetochores (PubMed:18936247). Its function related to the spindle assembly machinery and kinetochore-microtubule attachments likely depends on its association in the mitotic RZZ complex (PubMed:18936247). The RZZ complex recruits the spindly-like protein spdl-1 to kinetochores (PubMed:18765790, PubMed:18936247). 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:9298984). Component of the RZZ complex composed of rod-1, czw-1 and zwl-1. Localizes to the kinetochore during nuclear envelope breakdown and remains there until the metaphase-anaphase transition. Localization of the RZZ complex to kinetochores is dependent upon knl-1. RNAi-mediated knockdown largely results in sterility (PubMed:9298984, PubMed:18765790, PubMed:19109417). RNAi-mediated knockdown also results in a high incidence of embryonic lethality in the embryos produced and defects in mitosis which include the formation of chromatin bridges in between sister chromatids during anaphase (PubMed:9298984). In addition, there is reduced localization of the spindly-like protein spdl-1 to kinetochores, but not to microtubules (PubMed:18936247). Belongs to the ZW10 family.