BUB3 is a non-essential gene whose product is involved in the spindle checkpoint (6, 7). The spindle checkpoint delays the onset of anaphase in cells with defects in mitotic spindle assembly or in the attachment of chromosomes to the spindle microtubules (see 8 for review; reference 9 describes defects detected by the checkpoint). The checkpoint works by inhibiting the activity of the anaphase promoting complex, thereby preventing the degradation of several cell cycle regulators (8). Bub3p is a substrate for the protein kinase Bub1p (7), and interacts physically with Mad3p (4). Like other spindle checkpoint mutants, bub3 loss-of-function mutants are sensitive to benomyl and cannot delay cell division in response to spindle depolymerization (6). Bub1p, Bub3p, Mad1p, Mad2p, Mad3p, and the protein kinase Mps1p act in a branch of the spindle checkpoint pathway that may prevent premature chromosome disjunction. A second branch involves Bub2p and Bfa1p, and may prevent cytokinesis prior to chromosome segregation (10, 11, 12, 13). Homologs of Bub3p have been identified in several organisms, including Drosophila, mouse and human (BUB3), and most have been shown to localize to kinetochores not attached to spindles (14, 2, 15, 16).

Last updated: 2005-07-01