Role of the ubiquitin system in epigenetic regulation

泛素是一种由76个氨基酸组成的小分子蛋白质，从酵母到人类都很保守。它可以通过一个称为泛素化的过程共价添加到数千种不同的蛋白质上，为细胞调节提供多样性和动力学。组蛋白是一组碱性核蛋白，其结合并组织线性DNA成称为核小体的结构单元，核小体进一步浓缩成染色质。组蛋白的泛素修饰直接参与许多重要的细胞功能，包括转录、DNA复制、修复和基因沉默，因此在细胞分裂、生长和分化的调节中起关键作用。这种组蛋白修饰的机制和参与这一过程的参与者的特征很差。我们研究计划的目标是了解组蛋白的泛素修饰在细胞调节中的机制和重要性。在本申请中，我们将重点阐明泛素系统参与组蛋白H2 A的泛素化。H2 A泛素化参与维持基因组完整性、发育模式、X染色体失活和维持干细胞的多能性。负责H2 A泛素化的蛋白质包括酶E1（活化酶）、E2（缀合酶）和E3（连接酶）的级联，其将泛素共价连接到H2 A的特定赖氨酸残基。通过蛋白质组学、生物化学和细胞学的方法，我们拟对H2 A泛素化的机制进行研究，揭示H2 A泛素化过程中各蛋白的作用，并了解H2 A泛素化在细胞调控中的作用。具体目标包括：（1）揭示H2 A在体外和体内泛素化所需的特异性酶;（2）表征H2 A泛素化的分子基础和这些酶在基因调控中的作用;（3）研究负责H2 A变体泛素化的特异性酶。通过研究这些酶如何工作，我们将更好地了解组蛋白泛素化的重要性，以及它如何参与不同生物过程中基因表达的调控。

Ubiquitin, a 76 amino acid small protein, is well conserved from yeast to humans. It can be covalently added onto thousands of different proteins through a process known as ubiquitination to provide diversity and dynamics to cell regulation. Histones are a group of basic nuclear proteins that bind and organize the linear DNA into the structural units called nucleosomes, which are further condensed into chromatin. Ubiquitin modification of histones is directly involved in many vital cellular functions including transcription, DNA replication, repair and gene silencing and therefore plays a critical role in the regulation of cell division, growth and differentiation. The mechanism of this histone modification and the players involved in this process are poorly characterized. The goal of our research program is to understand the mechanism and the importance of ubiquitin modification of histones in cellular regulation.***In this application, we will focus on elucidation of the ubiquitin system involved in ubiquitination of histone H2A. H2A ubiquitination is involved in the maintenance of genome integrity, developmental patterning, X-chromosome inactivation and maintenance of pluripotency of stem cells. The proteins responsible for H2A ubiquitination include a cascade of enzymes, E1 (activating enzyme), E2 (conjugating enzymes) and E3 (ligases), which covalently attaching ubiquitin to specific lysine residues of H2A. Through proteomic, biochemical and cellular approaches, we propose to characterize the mechanism of H2A ubiquitination, to reveal the roles of each protein player in this process and to understand the function of H2A ubiquitination in cellular regulation. Specific aims include: (1) to reveal specific enzymes required for H2A ubiquitination in vitro and in vivo; (2) to characterize the molecular basis of H2A ubiquitination and the roles of these enzymes in gene regulation; and (3) to investigate specific enzymes that are responsible for ubiquitination of the H2A variants. By studying how these enzymes work, we will gain a better understanding of the importance of histone ubiquitination and how it is involved in the regulation of gene expression in different biological processes.