MAD2L1BPwas identified as a binding protein of the MAD2 mitotic arrest deficient-like 1 (MAD2/MAD2L1). This protein may interact with the spindle checkpoint and coordinate cell cycle events in late mitosis. Alternatively spliced transcript variants encoding distinct isoforms have been observed. Upon the completion of spindle attachment, formation of the CMT2-MAD2 complex coincides with dissociation of the p55CDC-MAD2 complex. Overexpression of CMT2 in cells arrested by the spindle checkpoint causes premature destruction of securin and allows exit from mitosis without chromosome segregation. Depletion of CMT2 induces cell death following a transient delay in the onset of anaphase. These results indicate that CMT3 interacts with the spindle checkpoint and coordinates cell cycle events in late mitosis.