May function to silence the spindle checkpoint and allow mitosis to proceed through anaphase by binding MAD2L1 after it has become dissociated from the MAD2L1-CDC20 complex. Interacts with MAD2L1. During early mitosis, unevenly distributed throughout the nucleoplasm. From metaphase to anaphase, concentrated on the spindle. During the cell cycle, levels increase and then remain constant until late mitosis after which they drop. Belongs to the MAD2L1BP family.