Chromatin structure is dictated by nucleosome assembly and internucleosomal interactions. The tight wrapping of nucleosomes inhibits gene expression, but modifications to histone tails modulate chromatin structure, allowing for proper genetic function. The histone H4 tail is thought to play a large role in regulating chromatin structure. Here we investigated the structure of nucleosomes assembled with a tail-truncated H4 histone using Atomic Force Microscopy. We assembled tail-truncated H4 nucleosomes on DNA templates allowing for the assembly of mononucleosomes or dinucleosomes. Mononucleosomes assembled on nonspecific DNA led to decreased DNA wrapping efficiency. This effect is less pronounced for nucleosomes assembled on positioning motifs. Dinucleosome studies resulted in the discovery of two effects- truncation of the H4 tail does not diminish the preferential positioning observed in full-length nucleosomes, and internucleosomal interaction eliminates the DNA unwrapping effect. These findings provide insight on the role of histone H4 in chromatin structure and stability.
DNA sequence plays an important role in the assembly of nucleosomes, and DNA motifs with high specificity to nucleosomes have been identified. At the same time, important questions such as how the DNA sequence changes DNA wrapping and how the DNA sequence contributes to the interaction between the nucleosomes remain unclear. Here, we addressed these questions by comparing nanoscale properties of nucleosomes assembled on the highest nucleosome positioning sequence, the 601 motif, and essentially random DNA sequences. We used atomic force microscopy to measure the nucleosome positions and the DNA wrapping. The studies showed that nucleosomes assemble on the nonspecific sequence without any preference for position on DNA, but they wrap the same DNA length as DNA of the same length with the 601 sequence. Experiments with longer DNA containing the 601 motif along with nonspecific DNA, capable of forming dinucleosomes, revealed that dinucleosomes assembled on hybrid sequences show a preference for positioning near each other, with one always assembling on the 601 motif. These findings point to the interaction between the nucleosomes and suggest that internucleosomal interactions may play a large role in nucleosome positioning.—Stormberg, T., Stumme‐Diers, M., Lyubchenko, Y. L. Sequence‐dependent nucleosome nanoscale structure characterized by atomic force microscopy. FASEB J. 33, 10916–10923 (2019). http://www.fasebj.org
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