National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China; Key Laboratory of Epigenetic Regulation and Intervention, Chinese Academy of Sciences, Beijing 100101, China.
National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China; Key Laboratory of Epigenetic Regulation and Intervention, Chinese Academy of Sciences, Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Cell Rep. 2023 Sep 26;42(9):113134. doi: 10.1016/j.celrep.2023.113134. Epub 2023 Sep 13.
The organization and dynamics of chromatin fiber play crucial roles in regulating DNA accessibility for gene expression. Here we combine cryoelectron tomography (cryo-ET), sub-volume averaging, and 3D segmentation to visualize the in vitro and in vivo chromatin fibers folding by linker histone. We discover that an increased nucleosome repeat length and prolonged fiber length do not change the two-start helical architecture in reconstituted chromatin of homogeneous composition. Additionally, an isolated chromatin fiber with heterogeneous composition was observed, which includes short-range regions compatible with two-start helix. In vivo, sub-volume averaging reveals similar subunits of two-start helical architecture in transcriptionally inactive chromatin in frog erythrocyte nuclei. Strikingly, unambiguous DNA trajectories that displayed a zigzag pattern universally between alternate N/N+2 nucleosomes were further determined by cryo-ET with voltage phase plate. Therefore, these structural similarities suggest a general folding mode of chromatin induced by linker histone, and heterogeneous compositions mainly affect local conformation rather than changing the overall architecture.
染色质纤维的组织和动力学在调节 DNA 可及性以进行基因表达方面起着至关重要的作用。在这里，我们结合冷冻电子断层扫描（cryo-ET）、子体积平均和 3D 分割，可视化连接组蛋白介导的体外和体内染色质纤维折叠。我们发现，增加核小体重复长度和延长纤维长度不会改变同组成分重建成核小体中的双螺旋结构。此外，还观察到具有异质组成的孤立染色质纤维，其中包括与双螺旋相容的短程区域。在体内，子体积平均揭示了在蛙红细胞核中转录不活跃的染色质中类似的双螺旋结构亚基。引人注目的是，通过带有电压相板的 cryo-ET 进一步确定了在交替的 N/N+2 核小体之间普遍呈现之字形模式的明确 DNA 轨迹。因此，这些结构相似性表明连接组蛋白诱导的染色质的一般折叠模式，异质组成主要影响局部构象，而不是改变整体结构。
