Required for the execution of the mitotic checkpoint which monitors the process of kinetochore-spindle attachment and delays the onset of anaphase when this process is not complete. It inhibits the activity of the anaphase promoting complex by sequestering CDC20 until all chromosomes are aligned at the metaphase plate. Part of the mitotic checkpoint complex (MCC); interacts with MAD1, CDC20-1, CDC20-2 and CDC20-5. Interacts with BUBR1 at chromocenters and with BUB3.1. Interacts with EIF4B3 (PubMed:20706207). Cytoplasmic in interphase cells. Accumulates onto both kinetochores and the spindle microtubules in cell arrested in metaphase. Present in chromocenters. Associates with unattached kinetochores upon spindle assembly checkpoint (SAC) activation. The nucleus envelope association requires the presence of NUA. A number of isoforms are produced. According to EST sequences. Expressed in actively dividing tissues, early in organ development, in young leaves, lateral root primordia and root meristems. Cell cycle regulated expression with a distinct expression peak at the G2/M boundary. No visible phenotype when grown under normal growth conditions and stunted roots when grown in vitro in absence of sucrose. Belongs to the MAD2 family.