Bub1 and BubR1: at the Interface between Chromosome Attachment and the Spindle Checkpoint

The spindle checkpoint ensures genome fidelity by temporarily halting chromosome segregation and the ensuing mitotic exit until the last kinetochore is productively attached to the mitotic spindle. At the interface between proper chromosome attachment and the metaphase-to-anaphase transition are the mammalian spindle checkpoint kinases. Compelling evidence indicates that the checkpoint kinases Bub1 and BubR1 have the added task of regulating kinetochore-microtubule attachments. However, the debate on the requirement of kinase activity is in full swing. This minireview summarizes recent advances in our understanding of the core spindle checkpoint kinases Bub1 and BubR1 and considers evidence that supports and opposes the role of kinase activity in regulating their functions during mitosis.