Has a dual role in the cell cycle. In mitosis, it is involved in maintenance of cdc2 kinase activity. It is subsequently required for regulation of septum formation. Could be involved in maintenance of cdc2 kinase activity by preventing, directly or indirectly, the degradation of cyclin or the dephosphorylation of 'Thr-167' of cdc2. Belongs to the BUB2 family.