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Updated: Jul 31, 2025

Mass Spectrometry Analysis to Identify Ubiquitylation of EYFP-tagged CENP-A EYFP-CENP-A
Published on: June 10, 2020
Repression of CENP-A assembly in metaphase requires HJURP phosphorylation and inhibition by M18BP1
Julio C Flores Servin1, Rachel R Brown1, Aaron F Straight1
1Department of Biochemistry, School of Medicine, Stanford University, Stanford, CA, USA.
Abstract:
Centromeres are the foundation for mitotic kinetochore assembly and thus are essential for chromosome segregation. Centromeres are epigenetically defined by nucleosomes containing the histone H3 variant CENP-A. CENP-A nucleosome assembly is uncoupled from replication and occurs in G1, but how cells control this timing is incompletely understood. The formation of CENP-A nucleosomes in vertebrates requires CENP-C and the Mis18 complex which recruit the CENP-A chaperone HJURP to centromeres. Using a cell-free system for centromere assembly in X. laevis egg extracts, we discover two activities that inhibit CENP-A assembly in metaphase. HJURP phosphorylation prevents the interaction between HJURP and CENP-C in metaphase, blocking the delivery of soluble CENP-A to centromeres. Non-phosphorylatable mutants of HJURP constitutively bind CENP-C in metaphase but are not sufficient for new CENP-A assembly. We find that the M18BP1.S subunit of the Mis18 complex also binds to CENP-C to competitively inhibit HJURP's access to centromeres. Removal of these two inhibitory activities causes CENP-A assembly in metaphase.
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