Transcriptional Repression by Histone Amino Termini in Yeast

该项目的长期目标是了解组蛋白氨基末端，特别是组蛋白H3的氨基末端对体内转录抑制的贡献程度，并确定它们实现这一作用的机制。真核生物的DNA被包装成染色质，染色质的基本单位核小体由大约146个碱基对的DNA组成，包裹在组蛋白蛋白的核心上。有些令人惊讶的是，组蛋白的非结构化氨基末端的修饰被证明是一种广泛使用的基因调控手段。组蛋白不是核小体的重要结构成分。大量研究表明，在不同的细胞过程中，包括细胞周期控制、激素反应和发育过程中，组蛋白氨基末端的修饰性参与了转录调控。尽管取得了这一进展，但对组蛋白氨基末端影响转录调控的机制知之甚少。首席研究人员发现了两个例子，其中组蛋白H3氨基末端对酵母转录抑制至关重要。在第一个例子中，在没有诱导剂的情况下，H3氨基末端阻止CHA1启动子上的CHA4激活剂的激活。在第二个例子中，INO1基因在没有H3氨基末端的情况下被强烈去抑制，尽管目前对其机制知之甚少。首席研究人员还利用微阵列技术发现，H3氨基末端对基因表达具有广泛的、全基因组范围的抑制作用。这些发现为确定H3氨基末端抑制的具体机制提供了基础。此外，还将进行实验，以检验组蛋白H3和H4的氨基末端在组蛋白去乙酰基酶RPD3介导的抑制中的作用。DNA是所有生命的主控制器和信息库。在非细菌细胞中，DNA与染色质中的组蛋白结合。这些蛋白质帮助DNA适应细胞，并参与许多使用DNA的过程的调节，包括将DNA转录成RNA--DNA中信息的“读出”。首席研究员使用贝克酵母进行的研究旨在了解组蛋白蛋白的特定部分如何阻止特定基因在不应该转录的时候被转录。由于酵母和高等生物中染色质的基本转录机制和组成非常相似，这些发现将为所有非细菌生物的转录调控提供新的线索。

The long term goals of this project are to understand the extent to which the histone amino termini, especially that of histone H3, contribute to transcriptional repression in vivo, and to determine the mechanisms by which they do so. Eukaryotic DNA is packaged into chromatin, and the fundamental unit of chromatin, the nucleosome, consists of about 146 base pairs of DNA wrapped around a core of histone proteins. Somewhat surprisingly, modification of the unstructured amino termini of the histones, which are not an essential structural component of the nucleosome, has turned out to be a widely used means of gene regulation. Numerous studies have implicated transcriptional regulation via modifications of the histone amino termini in diverse cellular processes, including cell cycle control, hormone response, and development. In spite of this progress, little is known of the mechanisms by which the histone amino termini influence transcriptional regulation. The principal investigator has discovered two examples in which the histone H3 amino terminus is critical for transcriptional repression in yeast. In the first example, the H3 amino terminus prevents activation by the CHA4 activator at the CHA1 promoter in the absence of inducer. In the second example, the INO1 gene is strongly derepressed in the absence of the H3 amino terminus, although little is known about the mechanism at present. The principal investigator has also found, using micorarray technology, that the H3 amino terminus exerts a broad, genome-wide repressive effect on gene expression. These findings serve as a basis to determine specific mechanisms for repression by the H3 amino terminus. In addition, experiments will be done to examine the contribution of the amino termini of histones H3 and H4 as targets in repression mediated by the histone deacetylase RPD3.DNA is the master controller and information reservoir for all of life. In non-bacterial cells, DNA is bound to histone proteins in chromatin. These proteins help the DNA fit inside the cell and participate in regulation of many processes that use DNA, including the transcription of DNA into RNA-the "readout" of the information in DNA. Studies by the principal investigator, using baker's yeast, are aimed at understanding how specific parts of the histone proteins prevent particular genes from being transcribed when they are not supposed to be. Because the basic mechanisms of transcription and components of chromatin are very similar in yeast and higher organisms, these findings will shed new light on transcriptional regulation in all non-bacterial organisms.