Structural and functional analysis of the yeast heterochromatin complex SIR

真核生物基因组被包装成不同的染色质结构域，在控制DNA的复制、转录、DNA修复和染色体分离等过程中起着至关重要的作用。大的基因组区域呈现一种称为异染色质的抑制性结构，它是由异染色质蛋白建立的，它与核小体结合并以未知的机制抑制转录。在高等真核生物中，这些区域通常位于端粒和着丝粒上，端粒是它们防止降解和重组的地方，着丝粒是染色体正确分离的重要部位。在发芽酵母HML和HMR以及端粒上发现了一种异染色质的原型。这些位点异染色质的建立和形成是由沉默信息调节(SIR)复合体介导的，SIR复合体由依赖NAD+的组蛋白脱乙酰酶(HDAC)Sir2和组分Sir3和Sir4组成。对SIR介导的抑制的详细机制理解需要复杂的分子知识.然而，虽然有SIR综合体个别部分的信息，但整个SIR综合体的结构缺失。在这个项目中，Ehrenhofer-Murray和Spahn实验室的目标是解决SIR复合体的自由形式以及它与核小体结合时的结构。我们将把这些结构目标与遗传实验相结合，以评估该结构(S)与酵母细胞沉默的功能相关性。这项工作将具有很高的相关性，因为它将允许对SIR情结如何实现镇压的结构和机械方面的新见解。

The packaging of eukaryotic genomes into functionally distinct chromatin domains plays a crucial role in controlling all processes on DNA like replication, transcription, DNA repair and chromosome segregation. Large genomic regions assume a repressive structure termed heterochromatin, which is established by heterochromatin proteins that bind to the nucleosomes and inhibit transcription by yet unknown mechanisms. In higher eukaryotes, such regions typically are found at the telomeres, where they prevent degradation and recombination, and centromeres, where they are important for proper chromosome segregation. An archetypal form of heterochromatin is found in the budding yeast Saccharomyces cerevisiae at the silent mating-type loci HML and HMR, and at the telomeres. The establishment and formation of heterochromatin at these loci is mediated by the silent information regulator (SIR) complex, which consists of the NAD+-dependent histone deacetylase (HDAC) Sir2 and the components Sir3 and Sir4. A detailed mechanistic understanding of SIR-mediated repression requires molecular knowledge the complex. However, while information is available for individual parts of the SIR complex, a structure of the complete SIR complex is missing. In this project, the Ehrenhofer-Murray and Spahn labs aim to solve the structure of the SIR complex in its free form as well as when it is bound to nucleosomes. We will combine these structural aims with genetic experiments to assess the functional relevance of the structure(s) for silencing in yeast cells. This work will be of high relevance, because it will allow novel structural and mechanistic insights into how repression by the SIR complex is achieved.