MS-Figues-final.pptx

Taking advantage of an in situ nucleosome stability assay based on the exposure of agarose-embedded nuclei to a concentration series of salt we could distinguish H2A.Z-nucleosomes at transcription start sites and in heterochromatin based on their stability features, what appeared to be determined by the alternative molecular engagements of the C-terminal tail of the histone variant (Imre et al., Nature Communications, 2024). Using a DT40 cell line pair expressing the human H2A.Z1 or its C-terminally truncated version, we demonstrate here that the stability of these nucleosomes is tail-dependent also through the spectacles of intercalator sensitivity, raising the possibility that the tail may bind to DNA in a superhelicity-dependent fashion. In line with this hypothesis, binding of a fluorescent dye-labeled H2A.Z-tail-nonapeptide to superhelical plasmid DNA could be detected by fluorescence correlation spectroscopy, while binding to the circularized plasmid, or in the case of a scrambled nonapeptide, were barely detectable. The DNA topology-dependent binding of the unstructured H2A.Z C-terminus, by affecting nucleosome stability, may be of functional significance in various roles of the histone variant, demonstrating the strong interplay between DNA topology and nucleosome stability and exemplifying how it may be exploited by the cell for regulatory purposes.