Assembly of Drosophila Centromeric Nucleosomes Requires CID Dimerization

SummaryCentromeres are essential chromosomal regions required for kinetochore assembly and chromosome segregation. The composition and organization of centromeric nucleosomes containing the essential histone H3 variant CENP-A (CID in Drosophila) is a fundamental, unresolved issue. Using immunoprecipitation of CID mononucleosomes and cysteine crosslinking, we demonstrate that centromeric nucleosomes contain CID dimers in vivo. Furthermore, CID dimerization and centromeric targeting require a residue implicated in formation of the four-helix bundle, which mediates intranucleosomal H3 dimerization and nucleosome integrity. Taken together, our findings suggest that CID nucleosomes are octameric in vivo and that CID dimerization is essential for correct centromere assembly.

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► Drosophila centromeric nucleosomes contain two copies of CID
► CID dimerization requires a critical residue for the four-helix bundle structure
► CID dimerization is essential for normal centromeric localization in vivo