Model for Bub3–BubR1 function on the tether/DNA breaks. The BubR1–Bub3 complex sequesters Fzy on broken chromosomes from prometaphase to late anaphase, preventing activation of the APC/C locally and transiently. This inhibition may prevent the APC/C-dependent degradation of a key factor (pink square with question mark) required to maintain the two broken fragments tethered and to facilitate their proper segregation. In bubR1-KEN or fzy-DYY* mutants, the Fzy-mediated activation of the APC/C around the broken fragments allows the premature degradation of the unknown factor, which impairs the tethering of the broken fragments and their correct segregation.