Figure 4.

A schematic diagram depicting a bifurcation of the mitotic checkpoint pathway. This model hypothesizes that defects in spindle assembly can potentially prevent two mitotic events: chromosome attachment to the spindle (a); and anaphase spindle elongation (b). A defect in a may be monitored at the kinetochores and activates a set of mitotic checkpoint proteins that prevent sister chromatid separation by blocking degradation of chromosome cohesion factors such as Pds1. A defect in b may be monitored at the spindle pole bodies through Bub2 and Bfa1, which prevent cytokinesis by blocking the degradation of mitotic cyclins such as Clb2.