H2A.Z交换反应中控制底物核小体特异性的分子机制

核小体核心颗粒由四种常规组蛋白或组蛋白变体组成。H2A.Z是高等真核生物必需的组蛋白变体，在基因转录调控等生命进程中发挥重要作用。染色质重构复合物SWR1/SRCAP催化H2A.Z-H2B替换染色质中的H2A-H2B，实现H2A.Z的染色质组装。SWR1/SRCAP的催化活性依赖于两种底物H2A核小体和H2A.Z-H2B的同时激活，但是决定H2A核小体底物特异性的机制尚缺乏系统研究。在前期工作中，项目申请人发现底物H2A与产物H2A.Z核小体的结构稳定性差异（内在因素），以及Swc2/YL1特异地作用并去稳定H2A核小体（外在因素）对决定底物核小体特异性起重要作用。本项目利用单分子力谱和多种生化技术手段，深入研究底物核小体和SWR1的重要亚基（Swc2/YL1）如何通过控制、识别和调节核小体结构稳定性来决定核小体底物特异性的分子机制。本研究对于阐明H2A.Z的染色质组装机制具有重要意义。

The nucleosome core particle is composed of four core histone proteins or their variants. H2A.Z is an essential histone variant in higher eukaryotes and plays important roles in gene transcription, genome stability and DNA damage response. H2A.Z is incorporated in chromatin by SWR1(SRCAP), an ATP-dependent, multi-component chromatin remodelling complex via a process called SWR1(SRCAP)-catalyzed histone H2A.Z replacement. Binding of both substrates, the canonical H2A nucleosome and the H2A.Z-H2B dimer, is essential for activation of SWR1, but how H2A nucleosome possess substrate selectivity for SWR1 has been unclear. In the previous work, the applicant found that the difference between structural stability of substrate H2A nucleosome and that of product H2A.Z nucleosome (intrinsic factors), and Swc2/YL1 specifically destabilizing H2A nucleosomes (exogenous factors), play an important role in determining the specificity of the substrate nucleosome. Here, by applying single-molecule force spectroscopy and other biochemical approaches, we study how the substrate nucleosome and SWR1(SRCAP) subunit (Swc2/YL1) control, recognize and regulate nucleosomal stability to reveal the molecular mechanisms controlling the specificity of substrate nucleosome in H2A.Z exchange. The knowledge we gain in this study is critical to understanding the mechanism by which H2A.Z incorporates into the chromatin.