Molecular basis for Cdk1‐regulated timing of Mis18 complex assembly and CENP‐A deposition

Abstract

The centromere, a chromosomal locus that acts as a microtubule attachment site, is epigenetically specified by the enrichment of CENP ‐A nucleosomes. Centromere maintenance during the cell cycle requires HJURP ‐mediated CENP ‐A deposition, a process regulated by the Mis18 complex (Mis18α/Mis18β/Mis18 BP 1). Spatial and temporal regulation of Mis18 complex assembly is crucial for its centromere association and function. Here, we provide the molecular basis for the assembly and regulation of the Mis18 complex. We show that the N‐terminal region of Mis18 BP 1 spanning amino acid residues 20–130 directly interacts with Mis18α/β to form the Mis18 complex. Within Mis18α/β, the Mis18α MeDiY domain can directly interact with Mis18 BP 1. Mis18α/β forms a hetero‐hexamer with 4 Mis18α and 2 Mis18β. However, only two copies of Mis18 BP 1 interact with Mis18α/β to form a hetero‐octameric assembly, highlighting the role of Mis18 oligomerization in limiting the number of Mis18 BP 1 within the Mis18 complex. Furthermore, we demonstrate the involvement of consensus Cdk1 phosphorylation sites on Mis18 complex assembly and thus provide a rationale for cell cycle‐regulated timing of Mis18 assembly and CENP ‐A deposition. image The cell cycle‐dependent assembly of the Mis18 complex is essential for HJURP ‐mediated CENP ‐A deposition at centromeres. This study presents the molecular basis for how the Mis18 complex is assembled and how Cdk1 times the assembly. Mis18α/β forms a hetero‐hexamer comprising 4 copies of Mis18α and 2 copies of Mis18β. The Mis18 BP 1 N‐terminus interacts with the Mis18α/β hetero‐hexamer via the MeDiY hetero‐dimer to form a hetero‐octameric assembly. Consensus Cdk1 phosphorylation sites within Mis18 BP 1 are involved in complex formation.