Mitotic checkpoint protein BUB3,( BUB3), is a saved component of the mitotic spindle assembly complex (MCC). The encoded protein has 4 WD repeat domains and has a similar sequence as the yeast BUB3 protein. BUB3 is vital for the kinetochore localization of BUB1 and BUBR1. BUB3 participates in the central spindle checkpoint pathway that operates during early embryogenesis. Furthermore BUB3 has a part in regulating the establishment of correct kinetochore-microtubule attachments.