Budding yeast CENP-A^Cse4 interacts with the N-terminus of Sgo1 and regulates its association with centromeric chromatin

Shugoshin is an evolutionarily conserved protein, which is involved in tension sensing on mitotic chromosomes, kinetochore biorientation, and protection of centromeric (<i>CEN</i>) cohesin for faithful chromosome segregation. Interaction of the C-terminus of Sgo1 with phosphorylated histone H2A regulates its association with <i>CEN</i> and pericentromeric (peri-<i>CEN</i>) chromatin, whereas mutations in histone H3 selectively compromise the association of Sgo1 with peri-<i>CEN</i> but not <i>CEN</i> chromatin. Given that histone H3 is absent from <i>CEN</i> and is replaced by a histone H3 variant CENP-A^Cse4, we investigated if CENP-A^Cse4 interacts with Sgo1 and promotes its association with the <i>CEN</i> chromatin. In this study, we found that Sgo1 interacts with CENP-A^Cse4 <i>in vivo</i> and <i>in vitro</i>. The N-terminus coiled-coil domain of Sgo1 without the C-terminus (<i>sgo1-NT</i>) is sufficient for its interaction with CENP-A^Cse4, association with <i>CEN</i> but not the peri-<i>CEN</i>, and this <i>CEN</i> association is cell cycle dependent with maximum enrichment in mitosis. In agreement with the role of CENP-A^Cse4 in <i>CEN</i> maintenance of Sgo1, depletion of CENP-A^Cse4 results in the loss of Sgo1 and <i>sgo1-NT</i> from the <i>CEN</i> chromatin. The N-terminus of Sgo1 is required for genome stability as a mutant lacking the N-terminus (<i>sgo1-CT</i>) exhibits increased chromosome missegregation when compared to a <i>sgo1-NT</i> mutant. In summary, our results define a novel role for the N-terminus of Sgo1 in CENP-A^Cse4 mediated recruitment of Sgo1 to <i>CEN</i> chromatin for faithful chromosome segregation.