Catalytic domain of the Serine/Threonine kinase, Vertebrate Spindle assembly checkpoint protein BubR1
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. BubR1 (Budding uninhibited by benzimidazoles R1) is also called Bub1 beta (Bub1b). It contains an N-terminal Bub1/Mad3 homology domain essential for Cdc20 binding and a C-terminal kinase domain. It is involved in SAC, a surveillance system that delays metaphase to anaphase transition by blocking the activity of APC/C (the anaphase promoting complex) until all chromosomes achieve proper attachments to the mitotic spindle, to avoid chromosome missegregation. BubR1 inhibits APC/C through direct binding. It also plays an important role in stabilizing kinetochore-microtubule attachments. Mutant mice expressing only 10% normal BubR1 protein are viable and develop into adult mice, but display many early aging-associated phenotypes including reduced lifespan, muscle atrophy, cataracts, impaired wound healing, and infertility. The BubR1 subfamily is part of a larger superfamily that includes the catalytic domains of other protein STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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