Faithful chromosome segregation during cell division relies on the centromere, a unique chromosomal locus that ensures proper kinetochore assembly and microtubule attachment. Unlike most chromosomal regions, the centromere is not defined by a specific DNA sequence but by the presence of the histone H3 variant CENP-A, which replaces canonical H3 within centromeric nucleosomes1,2,3,4,5,6. The incorporation of CENP-A is both necessary and sufficient for centromere function, and its propagation across cell generations underlies the epigenetic inheritance of the centromere position2,7,8,9. Despite substantial progress in understanding the CENP-A nucleosome structure and centromere identity maintenance, the specific structural features underlying this process remain incompletely defined. A long-standing controversy has surrounded the structural nature of the CENP-A nucleosome—whether it adopts a canonical octameric configuration similar to histone H3 nucleosomes or instead forms a noncanonical nucleosome such as a hemisome, composed of single subunits of H2A, H2B, CENP-A, and H410,11,12,13,14,15. Early biochemical and biophysical studies suggested that the CENP-A nucleosome might exhibit noncanonical, tetrameric arrangements, raising the possibility that hemisomes could represent a centromere-specific nucleosome form10,13,16. Subsequent reports proposed that CENP-A nucleosomes might exist as tetramers rather than octamers in certain cell-cycle states17,18, whereas other studies argued that the native form adopts the canonical octameric...

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