It is important to note that this model is not applicable to SAC regulation in higher order organisms, including animals. A main facet of the mechanical switch mechanism is that in "S. cerevisiae" the structure of the kinetochore only allows for attachment of one microtubule. Kinetochores in animals, on the other hand, are much more complex meshworks that contain binding sites for a multitude of microtubules. Microtubule attachment at all of the kinetochore binding sites is not necessary for deactivation of the SAC and progression to anaphase. Therefore, microtubule-attached and microtubule-unattached states coexist in the animal kinetochore while the SAC is inhibited. This model does not include a barrier that would prevent Mps1 associated with an attached kinetochore from phosphorylating Spc105 in an adjacent unattached kinetochore. Furthermore, the yeast Dam1/DASH complex is not present in animal cells.