Has a dual function in spindle-assembly checkpoint signaling and in promoting the establishment of correct kinetochore-microtubule (K-MT) attachments. Promotes the formation of stable end-on bipolar attachments. Necessary for kinetochore localization of BUB1. The BUB1/BUB3 complex plays a role in the inhibition of anaphase-promoting complex or cyclosome (APC/C) when spindle-assembly checkpoint is activated and inhibits the ubiquitin ligase activity of APC/C by phosphorylating its activator CDC20. This complex can also phosphorylate MAD1L1 (By similarity). Regulates chromosome segregation during oocyte meiosis. Interacts with BUB1 and BUBR1. The BUB1/BUB3 complex interacts with MAD1L1. Interacts with ZNF207/BuGZ; leading to promote stability and kinetochore loading of BUB3 (By similarity). Starts to localize at kinetochores in prometaphase I (Pro-MI) stage and maintains the localization until the metaphase I-anaphase I (MI-AI) transition. Poly-ADP-ribosylated by PARP1. Belongs to the WD repeat BUB3 family.