Biology Faculty, Lomonosov Moscow State University, Moscow 119234, Russia.
Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow 117997, Russia.
Int J Mol Sci. 2023 Jul 28;24(15):12127. doi: 10.3390/ijms241512127.
Formation of compact dinucleosomes (CODIs) occurs after collision between adjacent nucleosomes at active regulatory DNA regions. Although CODIs are likely dynamic structures, their structural heterogeneity and dynamics were not systematically addressed. Here, single-particle Förster resonance energy transfer (spFRET) and electron microscopy were employed to study the structure and dynamics of CODIs. spFRET microscopy in solution and in gel revealed considerable uncoiling of nucleosomal DNA from the histone octamer in a fraction of CODIs, suggesting that at least one of the nucleosomes is destabilized in the presence of the adjacent closely positioned nucleosome. Accordingly, electron microscopy analysis suggests that up to 30 bp of nucleosomal DNA are involved in transient uncoiling/recoiling on the octamer. The more open and dynamic nucleosome structure in CODIs cannot be stabilized by histone chaperone Spt6. The data suggest that proper internucleosomal spacing is an important determinant of chromatin stability and support the possibility that CODIs could be intermediates of chromatin disruption.
致密二联体（CODIs）的形成发生在活性调节 DNA 区域相邻核小体碰撞之后。尽管 CODIs 可能是动态结构，但它们的结构异质性和动力学尚未得到系统解决。在这里，采用单粒子Förster 共振能量转移（spFRET）和电子显微镜研究了 CODIs 的结构和动力学。溶液和凝胶中的 spFRET 显微镜显示，在 CODIs 的一部分中，核小体 DNA 与组蛋白八聚体的解旋程度相当大，这表明在存在相邻紧密定位的核小体的情况下，至少一个核小体不稳定。因此，电子显微镜分析表明，多达 30 bp 的核小体 DNA 参与八聚体上的瞬时解旋/缠绕。在 CODIs 中，更开放和动态的核小体结构不能被组蛋白伴侣 Spt6 稳定。这些数据表明适当的核小体间间隔是染色质稳定性的重要决定因素，并支持 CODIs 可能是染色质破坏的中间体的可能性。
