核小体是真核细胞染色体结构第一个重要的结构层次，其组装和拆解的动力学路径直接影响染色体的整体结构。目前高精度的核小体静态结构已经解析出，但其结构形成的动力学机制还不清楚，亟待实验提供直接的证据。本项目中，我们将设计制备可连接两个微球的DNA样品，利用高分辨率的磁镊单分子设备，并结合单分子荧光技术和原子力显微镜，实时测量核小体动态组装和拆解过程中DNA长度和转动的变化。这样的实验方案能够分辨出核小体动态结构的细微变化，帮助我们回答核小体领域中两个关键的问题：（1）核小体组装和拆解的动力学路径；（2）DNA的扭力对核小体以及核小体链的影响。在此基础上，我们将系统研究组蛋白的不同变体、DNA和组蛋白的化学修饰、核小体辅助因子以及重构因子等因素对核小体结构稳定性影响。本项目的开展对理解核小体的组装和拆解,染色体三维高级结构，以及DNA复制、转录等生命过程有着积极重要的意义。

Nucleosome is the basic structure of eukaryotic chromatin. The dynamics of nucleosome assembly and disassembly have important effects on higher level structures of chromatin. Although the nucleosome high resolution static structure has been resolved, the dynamics of nucleosome assembly and disassembly are unclear.To investigate this nucleosome dynamics,we first design new DNA samples which can combine two micro-beads. And we will record the length and rotation of DNA simultaneously by magnetic tweezers, which will show the structure changes of nuclesome in details and help us judge the status of combination between DNA and histones. The experiments will assit us to answer two critical questions about nucleosome. The first question is what is the dynamical path of nucleosome assembly and disassembly. The second one is what is the effects of DNA twist on nucleosome's structure. Based on these studies, we will check the stability of nuclsome for different histone variants, the chemical modification of DNA and histones,the nucleosome factors such as NAP1 and ACF. The investigation of dynamics of nucleosome assembly and disassembly will help us to understand the structure of nucleosome, three-dimention genome and the process of DNA replication and transcription.