Metaphase checkpoint controls sense abnormalities in chromosome alignment during mitosis and prevent progression to anaphase until proper alignment has been attained. A number of proteins, including Mitotic arrest deficiency protein 2 (MAD2), Budding uninhibited benzimidazole 1 (BUB1) and Budding uninhibited benzimidazole receptor 1 (BUBR1), have been implicated in the metaphase checkpoint control in mammalian cells. BUB1 and BUBR1 both localize to kinetochores during mitosis, suggesting that they play a role in delaying anaphase until all chromosomes achieve correct, bipolar attachment to the spindle. BUB1 and BUBR1 respond differently to spindle dynamics, they are part of a common complex during mitosis and BUB1 and BUBR1 may integrate different 'spindle assembly signals' into a single signal which can then be interpreted by downstream cell cycle regulators.Synonyms: BUB1 beta, BUBR1, MAD3/BUB1-related protein kinase, MAD3L, Mitotic checkpoint kinase MAD3L, Mitotic checkpoint serine/threonine-protein kinase BUB1 beta, Protein SSK1