Central component of the spindle assembly checkpoint which is a feedback control that prevents cells with incompletely assembled spindles from leaving mitosis. Thought to be recruited to unattached kinetochores by MAD1. During checkpoint activity, MAD2 is relayed from the MAD1-MAD2 complex to the mitotic checkpoint complex (MCC). MCC and presumably the MAD2-CDC20 subcomplex inhibit the ubiquitin ligase activity of the anaphase promoting complex/cyclosome (APC/C) by preventing its activation by CDC20. Component of the mitotic checkpoint complex (MCC) which consists of MAD2, MAD3, BUB3 and CDC20, and of the MAD2-CDC20 subcomplex, both of which appear to be assembled during mitoisis independently of the kinetochore. In mitose-arrested cells, MAD2-CDC20 occurs in a larger amount than MCC. Interacts with CDC20 and BUB3. Present with 1110 molecules/cell in log phase SD medium. Belongs to the MAD2 family.