Central component of the spindle assembly checkpoint which is a feedback control that prevents cells with incompletely assembled spindles from leaving mitosis. Plays a key role in virulence, probably through cell cycle checkpoint functions, especially those monitoring the integrity of DNA and chromosome segregation, which might be required for the pathogen to repair damage caused by host defense. Component of the mitotic checkpoint complex (MCC). Quickly loses viability when treated with nocodazole, which causes disassembly of mitotic spindles. Exhibits increased frequency of chromosome loss and greatly reduced virulence in mice. Belongs to the MAD2 family.