Structural diversity of noncanonical nucleosomes: Functions in chromatin

In eukaryotes, genomic DNA is compacted into chromatin, with nucleosomes acting as its basic structural units. In addition to canonical nucleosomes, noncanonical nucleosomes, such as hexasomes, H3-H4 octasomes, and overlapping dinucleosomes, exhibit alternative histone compositions and play key roles in chromatin remodeling, transcription, and replication. Recent cryo-electron microscopy (cryo-EM) studies have elucidated the structural details of these noncanonical nucleosomes and their interactions with histone chaperones and chromatin remodelers. This review highlights recent advances in the structural and functional understanding of noncanonical nucleosomes and their roles in maintaining chromatin integrity and facilitating transcriptional dynamics.