Cryo-EM structures of CENP-A nucleosomes isolated from human cells.

Cryo-EM reveals that human CENP-A nucleosomes in cells assemble as histone octamers with DNA wrapped in a left-handed superhelix, confirming the octameric model.

• Why it matters: Understanding the native structure of CENP-A nucleosomes is crucial for elucidating centromere identity and chromosome segregation, addressing gaps left by studies on reconstituted nucleosomes.
• What they did: Using chromatin immunoprecipitation combined with cryogenic electron microscopy, the study determined the structures of two distinct human CENP-A nucleosomes directly from cells, without crosslinking.
• The result: Both homotypic and heterotypic CENP-A nucleosomes maintain key structural features, including the shortened N-terminal α-helix and RG loop, defining their organization in cellular chromatin.