Chromatin Modification by Histone Ubiquitination

描述（申请人提供）：通过组蛋白共价修饰改变染色质是基因表达调控的核心。乙酰化修饰是组蛋白共价修饰的最佳方式，对基因表达具有广泛的影响。组蛋白磷酸化对于转录激活、有丝分裂和减数分裂期间染色体的凝聚以及细胞分裂的调节是重要的。组蛋白甲基化和单泛素化在基因表达调控中的作用最近被揭示。 多年来，我们一直在研究MLL蛋白在人类白血病发展中的作用。Setl蛋白。酿酒酵母与人MLL密切相关。我们和其他人已经纯化了一种包含Setl的多蛋白复合物，我们称之为COMPASS。我们已经证明，COMPASS是所需的赖氨酸4在组蛋白H3的氨基末端尾部的甲基化，这组蛋白修饰是位于染色体端粒附近的基因的表达沉默所需的。我们发现，招募COMPASS优先发生在启动子和早期延伸聚合酶。在对酵母基因组中组蛋白H3甲基化所必需的基因产物的调查中，我们发现泛素结合酶Rad 6及其可能的E3连接酶Bre 1和Paf 1复合物是组蛋白H3的赖氨酸4和赖氨酸79甲基化所必需的。由于Rad 6催化组蛋白H2 B的赖氨酸123的单泛素化，因此组蛋白H2 B的这种修饰可能是指导COMPASS催化组蛋白H3的K4甲基化的信号。我们希望通过Rad 6，Brel和Pafl复合物来定义组蛋白泛素化的机制，以及它们在通过单泛素化修饰组蛋白来调节基因表达中的作用。我们的具体目标是： 目标1：了解Rad 6/Bre 1如何将组蛋白H2 B的赖氨酸123单泛素化限制在基因的启动子区域，并了解此事件对基因调控的影响。 目标二：了解组蛋白H2 B的单泛素化是否作为组蛋白甲基转移酶COMPASS的募集和/或激活的信号。 目的3：阐明H2 B去泛素化的分子机制。 这些研究承诺：i）提高我们对组蛋白单泛素化在转录调节中的作用的理解，ii）阐明泛素化如何以及为何优先在启动子处发生，iii）揭示启动子处组蛋白的泛素化是否、为何以及如何发出组蛋白甲基化信号，以及iv）阐明酵母Setl和人MLL中保守的Set结构域在血液恶性肿瘤的发展和发病机制中的作用。

DESCRIPTION (provided by applicant): Alteration of chromatin by covalent modification of histone proteins is central to regulation of gene expression. Acetylation, the best-characterized covalent modification of histones, has wide-ranging effects on gene expression. Histone phosphorylation is important for transcriptional activation, condensation of chromosomes during mitosis and meiosis, and regulation of cell division. Roles for histone methylation and monoubiquitination in the regulation of gene expression have recently been revealed. For several years we have been studying the role of the MLL protein in the development of human leukemia. Setl protein of S. cerevisiae is closely related to human MLL. We and others have purified a Setl containing multiprotein complex that we call COMPASS. We have demonstrated that COMPASS is required for methylation of lysine 4 in the amino-terminal tail of histone H3, and that this histone modification is required for silencing of expression of genes located near chromosome telomeres. We found that recruitment of COMPASS occurs preferentially at the promoter and with the early elongating polymerase. In a survey of the yeast genome for gene products necessary for histone H3 methylation, we discovered that the ubiquitin-conjugating enzyme Rad6, together with its likely E3 ligase, Bre1, and the Paf1 complex are required for methylation of lysine 4 and lysine 79 of histone H3. Since Rad6 catalyzes monoubiquitination of lysine 123 of histone H2B, this modification of histone H2B may be a signal that directs COMPASS to catalyze methylation of K4 of histone H3. We wish to define the mechanism of histone ubiquitination by Rad6, Brel, and the Pafl complex and their roles in regulation of gene expression via histone modifications by monoubiqutination. Our specific aims are: Aim 1: To understand how monoubiquitination of lysine 123 of histone H2B by Rad6/Bre1 is limited to the promoter regions of genes, and learn about the consequences of this event for gene regulation. Aim 2: To learn if monoubiquitination of histone H2B serves as a signal for the recruitment and/or activation of the histone methyltransferase COMPASS. Aim 3: To define the molecular mechanism ofdeubiquitination of historic H2B. These studies promise to: i) improve our understanding of the role of histone monoubiquitination in regulation of transcription, ii) shed light on how and why ubiquitination occurs preferentially at promoters, iii) reveal if, why, and how ubiquitination of histones at promoters signals histone methylation, and iv) shed light on the role of the conserved Set domain in yeast Setl and human MLL in development and pathogenesis of hematological malignancies.