The Spc105/Kre28 Complex Promotes Mitotic Error Correction by Outer Kinetochore Recruitment of Ipl1/Sli15.

Kinetochores link chromosomes to dynamic microtubules of the mitotic spindle. To ensure equal chromosome segregation, sister chromatids must achieve biorientation. The conserved kinase Aurora B phosphorylates outer kinetochore proteins on attachments lacking tension, allowing the re-establishment of new connections until biorientation is achieved. Aurora B localizes to the centromere as part of the chromosomal passenger complex (CPC), but the underlying recruitment pathways can be eliminated without disrupting biorientation. It therefore remains unclear how the kinase operates during error correction. Here, we identify the conserved Spc105/Kre28 complex as an outer kinetochore receptor of the Aurora kinase Ipl1 and its activator Sli15 in Saccharomyces cerevisiae. We show that mutations in the helix bundle domain of Spc105/Kre28 impair mitotic error correction, resembling the effects of ipl1 or sli15 mutants. The defects can be suppressed by the artificial recruitment of Ipl1. In biochemical experiments, Ipl1/Sli15 directly associates with Spc105/Kre28, and a conserved segment in the Sli15 central domain is crucially involved in the binding mechanism. These results have important implications for the mechanism of tension-dependent error correction during chromosome biorientation.