组蛋白修饰调控异染色质边界的分子机制

项目名称： 组蛋白修饰调控异染色质边界的分子机制

项目编号： No.30800628

项目类型： 青年科学基金项目

立项/批准年度： 2009

项目学科： 生物科学

项目作者： 周菁

作者单位： 中国科学院上海生命科学研究院

项目金额： 18万元

中文摘要： 真核生物的基因表达状态依赖于其在染色质上的定位。通常情况下，位于异染色质 的基因处于沉默状态而常染色质允许基因表达。染色质边界元件 (Chromatin Boundary element)及染色质修饰梯度（gradient of chromatin modification）帮助了限定异染色质和常染色质。我们在芽殖酵母中建立了一种筛选调控边界活性的复合物的方法，并验证了部分已知的调控蛋白。其中一种重要的组蛋白去乙酰化酶Rpd3调节边界活性的作用和分子机制引起了我们的极大兴趣。目前对芽殖酵母中染色质边界调控蛋白的研究侧重于遗传学研究，几种调控理论相对独立且多基于推测，缺乏系统性。本项目旨在通过结合酵母遗传学、生物化学与分子生物学的研究方法，整合不同理论雏型，特别是从组蛋白修饰角度探讨Rpd3复合物调控染色质边界的机制，将人们对染色质沉默与表观遗传修饰之关系的认识从遗传学水平上升到分子水平。

中文关键词： 异染色质边界；组蛋白修饰；去乙酰化酶；沉默信息调节子

英文摘要： In the eukaryotic genome, transcriptionally silent chromatin tends to propagate along a chromosome and encroach upon adjacent active chromatin. The silencing machinery can be stopped by chromatin boundary elements. We performed a screen in Saccharomyces cerevisiae for proteins that may contribute to the establishment of a chromatin boundary. We found that disruption of histone deacetylase Rpd3p results in defective boundary activity, leading to a Sir-dependent local propagation of transcriptional repression. In rpd3D cells, the amount of Sir2p that was normally found in the nucleolus decreased and the amount of Sir2p found at telomeres and at HM and its adjacent loci increased, leading to an extension of silent chromatin in those areas. In addition, Rpd3p interacted directly with chromatin at boundary regions to deacetylate histone H4 at lysine 5 and at lysine 12. Either the mutation of histone H4 at lysine 5 or a decrease in the histone acetyltransferase (HAT) activity of Esa1p abrogated the silencing phenotype associated with rpd3 mutation, suggesting a novel role for the H4 amino terminus in Rpd3p-mediated heterochromatin boundary regulation. Together, these data provide insight into the molecular mechanisms for the anti-silencing functions of Rpd3p during the formation of heterochromatin boundaries.

英文关键词： heterochromatin boundary; histone modification; deacetylase; silent information regulator