Fig. 10. Model showing the temporal order and level of dependency of checkpoint proteins at the kinetochore. Bub1 acts as a master regulator for the assembly of checkpoint proteins at the kinetochore. The thick lines represent protein-protein interactions at the kinetochore but our data do not support the notion that the assembly pathway is a simple linear process. Therefore, other factors in addition to the linear pathway must also contribute to kinetochore targeting. One such factor might be Aurora B, which, as depicted by the thin lines, might cause priming of either the kinetochore and/or kinetochore proteins.