Cdk1 controls proteins involved chromosome segregation. Cdk1 controls chromosome cohesion by phosphorylating Pds1 and possibly the cohesin Scc1. Assembly of the mitotic spindle is also controlled by Cdk1, because it phosphorylates Spc42 and Mps1, which is important for SPB duplication, as well as Spc110, which may play a role in attachment of the SPB to the mitotic spindle. Cdk1 also prevents SPB re-duplication, but the molecular mechanism remains to be determined. Spindle positioning is mediated by Cdk1-dependent phosphorylation of Kar9, the SPB component Cnm67, and possibly Stu2. Later in the cell cycle Cdk1 phosphorylates Ase1, Bir1, Fin1 and Sli15 to modulate spindle stability and elongation.