The Spc105 ^Knl1 /Kre28 ^Zwint complex promotes mitotic error correction by outer kinetochore recruitment of the Ipl1 ^{Aurora B} kinase

Kinetochores link chromosomes to dynamic microtubules of the mitotic spindle. To ensure equal chromosome segregation, sister chromatids must attach to microtubules from opposing spindle poles, a configuration referred to as biorientation. To avoid chromosome missegregation the conserved kinase Aurora B phosphorylates outer kinetochore proteins on attachments lacking tension, allowing re-establishment of new connections until biorientation is achieved. While Aurora B localizes to the centromere and inner kinetochore as part of the chromosomal passenger complex (CPC), the underlying recruitment pathways can be eliminated without fully disrupting biorientation. It therefore remains unclear how the kinase operates during error correction and whether additional mechanisms may facilitate tension-dependent phosphorylation of substrate proteins.

In this study, we identify the conserved KMN subcomplex Spc105 ^Knl1 /Kre28 ^Zwint as an outer kinetochore receptor of the Aurora kinase Ipl1 in Saccharomyces cerevisiae . We show that mutations in the helical bundle domain of Spc105/Kre28 cause defective mitotic error correction, closely resembling the effects of ipl1 or sli15 mutants. In biochemical experiments we show that Ipl1/Sli15 directly associates with the KMN network via the Spc105/Kre28 subcomplex and that binding is inhibited by Ipl1 autophosphorylation. The phenotype of the kre28 mutant cells can be efficiently suppressed by artificial recruitment of Ipl1, demonstrating the importance of Ipl1 docking to the outer kinetochore. These results have important implications for the mechanism of tension-dependent error correction during chromosome biorientation.