BUB3

Mitotic checkpoint protein BUB3 is a protein that in humans is encoded by the BUB3 gene. Bub3 is a protein involved with the regulation of the Spindle Assembly Checkpoint (SAC); though BUB3 is non-essential in yeast, it is essential in higher eukaryotes. As one of the checkpoint proteins, Bub3 delays the irreversible onset of anaphase through direction of kinetochore localization during prometaphase to achieve biorientation. In directing the kinetochore-microtubule interaction, this ensures the proper (and consequently, bioriented) attachment of the chromosomes prior to anaphase. Bub3 and its related proteins that form the Spindle Assembly Checkpoint (SAC) inhibit the action of the Anaphase Promoting Complex (APC), preventing early anaphase entry and mitotic exit; this serves as a mechanism for the fidelity of chromosomal segregation.

Mitotic checkpoint protein BUB3 is a protein that in humans is encoded by the BUB3 gene. Bub3 is a protein involved with the regulation of the Spindle Assembly Checkpoint (SAC); though BUB3 is non-essential in yeast, it is essential in higher eukaryotes. As one of the checkpoint proteins, Bub3 delays the irreversible onset of anaphase through direction of kinetochore localization during prometaphase to achieve biorientation. In directing the kinetochore-microtubule interaction, this ensures the proper (and consequently, bioriented) attachment of the chromosomes prior to anaphase. Bub3 and its related proteins that form the Spindle Assembly Checkpoint (SAC) inhibit the action of the Anaphase Promoting Complex (APC), preventing early anaphase entry and mitotic exit; this serves as a mechanism for the fidelity of chromosomal segregation. ==Regulation== When the SAC is activated, the production of the Bub3-Cdc20 complex is activated. After kinetochore attachment is complete, the spindle checkpoint complexes (including the BubR1-Bub3) experience a decrease in concentration. Bub3 also acts as a regulator in that it affects binding of Mad3 to Mad2. Structural and sequence analysis indicated the existence of three conserved regions that are referred to as WD40 repeats. Mutation of one of these motifs has indicated an impaired ability of Bub3 to interact with Mad2, Mad3, and Cdc20. The structural data suggested that Bub3 acts as a platform that mediates the interaction of SAC protein complexes.

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