Seems to act in the pleiotropic control of cell division. Has a role in chromosome segregation by recruiting condensin and ark1 kinase to appropriate sites as the cell progresses through mitosis. Ark1 activity depends upon bir1 function and phosphorylation. Ark1 with bir1 function is required for full-scale association with kinetochores and formation of a complex with mad3. Interacts with ark1 and mad3 to form part of the mad2 complex involved in checkpoint activation. Interacts with the outer centromeric regions of the chromosomes during interphase. After chromatid separation moves to the middle of the spindle. Phosphorylated by ark1.