Differential nucleosome organization in human interphase and metaphase chromosomes [ChemMap]

Mitosis induces profound changes in chromosome structure, impacting nucleosome organization. Here, we employed chemical mapping to achieve single-base-pair resolution of nucleosome positioning in human interphase and metaphase chromosomes, unveiling distinct organizing principles between the two states. During interphase, we observe greater variability in internucleosome spacing, with a higher abundance of shorter linkers compared to metaphase, reflecting the genome's adaptability in accommodating nucleosome arrays for gene expression. Local analyses further uncover differential nucleosome landscapes at key euchromatin landmarks, including promoters, enhancers, and insulators, in each state. Moreover, we analyzed the relationship between DNA cyclizability and dyad positioning during mitosis. Our results indicate that in metaphase, nucleosomes exhibit significantly higher cyclizability around the dyad, whereas during interphase, nucleosomes more frequently position DNA with higher cyclizability in the nucleosome shoulder near regulatory genomic regions. Together, this study offers novel insights into the intricate interplay between DNA mechanics and nucleosome dynamics during mitosis.