Cell-Cycle-Dependent Structural Transitions in the Human CENP-A Nucleosome In Vivo

SummaryIn eukaryotes, DNA is packaged into chromatin by canonical histone proteins. The specialized histone H3 variant CENP-A provides an epigenetic and structural basis for chromosome segregation by replacing H3 at centromeres. Unlike exclusively octameric canonical H3 nucleosomes, CENP-A nucleosomes have been shown to exist as octamers, hexamers, and tetramers. An intriguing possibility reconciling these observations is that CENP-A nucleosomes cycle between octamers and tetramers in vivo. We tested this hypothesis by tracking CENP-A nucleosomal components, structure, chromatin folding, and covalent modifications across the human cell cycle. We report that CENP-A nucleosomes alter from tetramers to octamers before replication and revert to tetramers after replication. These structural transitions are accompanied by reversible chaperone binding, chromatin fiber folding changes, and previously undescribed modifications within the histone fold domains of CENP-A and H4. Our results reveal a cyclical nature to CENP-A nucleosome structure and have implications for the maintenance of epigenetic memory after centromere replication.

Graphical AbstractFigure optionsDownload high-quality image (188 K)Download as PowerPoint slideHighlights
► CENP-A nucleosomes oscillate between stable tetramers and stable octamers in human cells
► Structural oscillations are paralleled by changes in deposition of the chaperone HJURP
► CENP-A and H4 are acetylated at the transition point between tetramers and octamers
► Oscillations correlate with opening and closing of the CENP-A chromatin fiber