Performs two crucial functions during mitosis: it is essential for spindle-assembly checkpoint signaling and for correct chromosome alignment. Required for attachment of the kinetochores to the spindle microtubules. Directly links BUB1 and BUB1B to kinetochores. Part of the MIS12 complex, which may be fundamental for kinetochore formation and proper chromosome segregation during mitosis. Acts in coordination with CENPK to recruit the NDC80 complex to the outer kinetochore. Interacts with DSN1, MIS12, BUB1, BUB1B, NSL1 and ZWINT. Weakly expressed in interphase nuclei. Expression increases from prophase to late anaphase, but greatly diminishes from the telophase and cytokinesis to early G1 phase of cell cycle. Highly expressed in testis, where it is localized in germ cells, in particular in spermatocytes and in the pre-acrosome of round spermatids. Detected in the acrosome of ejaculated spermatozoa. Detected in adult thymus, bone marrow, colon, small intestine, appendix and placenta, and in fetal liver and thymus. A chromosomal aberration involving KNL1 is associated with acute myeloblastic leukemia (AML). Translocation t(11;15)(q23;q14) with KMT2A. May give rise to a KMT2A-KNL1 fusion protein. The disease is caused by variants affecting the gene represented in this entry.