Bub3 regulates the Ipl1/PP1 balance at the kinetochore, ensuring proper anaphase onset and chromosome segregation. (A) Graph of wild-type cells, cells with nuclear depletion of Bub3, and cells with nuclear depletion of Bub3 and Spc105. Those that have a nuclear depletion of Spc105 also express SPC105 or SPC105^RASA, under the meiosis-specific REC8 promoter, at the TRP1 or LEU2 locus. Rapamycin was added 7 h after the cells were resuspended in sporulation medium. Error bars represent SEM. At least 100 cells from two or more independent experiments per genotype were monitored. Asterisks indicate a statistically significant difference compared with wild-type cells (*, P < 0.05, Mann-Whitney test). (B) Graph of wild-type cells with nuclear depletion of Spc105 and cells with nuclear depletion of Bub3. Cells with nuclear depletion of Spc105 express SPC105 or SPC105^RVAF under the REC8 promoter for meiosis-specific expression, localized at the TRP1 or LEU2 locus. Cells expressing GLC7-SPC105^RASA produce a fusion protein of Glc7 and Spc105 under the control of the SPC105 promoter at the endogenous locus. Error bars represent SEM. At least 100 cells from two or more independent experiments per genotype were monitored. Asterisks indicate a statistically significant difference compared with wild-type cells (*, P < 0.05, Mann-Whitney test). (C) Model: Bub3 recruits and maintains Ipl1 at the kinetochore, which ensures proper meiotic chromosome segregation. This prevents PP1 from prematurely binding the kinetochore and premature APC/C activation, which ensures proper anaphase onset. aa, anchor away.