Figure 7.

Model for the role of pericentromeric cohesion in biorientation. (A) Cohesion establishment at pericentromeres mediated in part by Mcm21 helps to impose steric constraints on kinetochore orientation to ensure biorientation. Ipl1 senses tension and the bioriented attachments are stabilized. The pericentromeric region is depicted as the looped out regions of the chromosome. (B) In the absence of Mcm21, the decrease in pericentromeric cohesion may alter kinetochore geometry, making it more difficult for kinetochores to biorient and increasing the requirement for Ipl1 (left). The defect in pericentromeric cohesion may also reduce the cell's ability to sense tension properly and affect the regulation of Ipl1 and/or the stability of the MT–kinetochore attachments (left and right).