Phosphorylation of a borealin dimerization domain is required for proper chromosome segregation

NMR spectroscopy was used to determine the stoichiometry of the chromosomal passenger complex (CPC) and identify Mps1 phosphorylation site which modulated the dimerization state of borealin associated with the kinase aurora B within the CPC complex. The mutation of the single residue of borealin to alanine or valine which impaired the kinase aurora B activity during mitosis and caused chromosome segregation defects revealed that Mps1 regulated the CPC through a novel borealin domain.