Bub1 targeting to centromeres is sufficient for Sgo1 recruitment in the absence of kinetochores

Centromeric chromatin containing the histone H3 variant centromere protein A (CENP-A) directs kinetochore assembly through a hierarchical binding of CENPs, starting with CENP-C and CENP-T. Centromeres are also the chromosomal regions where cohesion, mediated by cohesin, is most prominently maintained in mitosis. While most cohesin dissociates from chromosome arms in prophase, Shugoshin 1 (Sgo1) prevents this process at centromeres. Centromeric localization of Sgo1 depends on histone H2A phosphorylation by the kinase Bub1, but whether additional interactions with kinetochore components are required for Sgo1 recruitment is unclear. Using the Xenopus egg cell-free system, we here show that both CENP-C and CENP-T can independently drive centromeric accumulation of Sgo1 through recruitment of Bub1 to the KNL1, MIS12, NDC80 (KMN) network. The spindle assembly checkpoint (SAC) kinase Mps1 is also required for this pathway even in the absence of checkpoint signaling. Sgo1 recruitment is abolished in chromosomes lacking kinetochore components other than CENP-A. However, forced targeting of Bub1 to centromeres is sufficient to restore Sgo1 localization under this condition.