Role of histone tails in gene expression and cellular functions

我在实验室的研究项目的主要目的是研究染色质如何影响基因调控过程。最近，我的实验室一直有兴趣了解H3和H4组蛋白尾巴如何调控基因表达和其他细胞过程。值得注意的是，非结构化的N端的组蛋白尾巴保存得非常好。组蛋白H3和H4尾部的序列最好地说明了这一点，从酵母到哺乳动物，它们几乎是100%保守的。组蛋白H3和H4的尾巴在其基本功能上是多余的，因为它们中的任何一个都可以在另一个存在的情况下被删除，但它们不能一起删除。此外，H3和H4尾部可以互换，分别位于H4和H3的核心上。几个实验室的研究表明，H3和H4尾巴对适当的基因调控和DNA修复是重要的，有人提出这一机制需要翻译后修饰(甲基化、乙酰化、磷酸化等)。位于组蛋白尾部的几个关键残基(赖氨酸、精氨酸、丝氨酸和苏氨酸)。由于尾内部和尾之间的功能冗余，这些残基中的每一个对于H3和H4尾的特定功能的重要性特别难以调查，因此，阐明特定残基与组蛋白H3和H4尾功能之间的联系将需要大量的点突变组合。为了解决这些复杂的问题，我的实验室建立了一个基因筛查，利用了H3和H4的N末端同时缺失是不可行的这一事实。用随机序列设计了一个含有N-末端尾巴的H3分子文库，并筛选了能够恢复H3-H4突变株活力的序列。我们成功地鉴定出合成尾巴，它们不仅恢复了活性，还增加了原始应变在某些压力条件下的适应性。因此，目前的研究计划将重点放在这些合成尾巴的生物化学和遗传学特征上，以揭示它们的作用机制。这些筛选方法已被证明在识别蛋白质-蛋白质相互作用和了解复杂机制方面非常有用。*特别是，我们将像对H3所做的那样，重点筛选H4 N末端尾巴，并使用蛋白质组学和遗传学方法来寻找这些合成的H3和H4组蛋白尾巴的直接功能靶点。**

Significant effort from my research program in my laboratory has been aimed at studying how chromatin affects the process of gene regulation. More recently, my laboratory has been interested in understanding how H3 and H4 histone tails can regulate gene expression and other cellular processes. Remarkably, the non-structured N-terminal histone tails are extremely well conserved. This is best illustrated with the sequence of the histone H3 and H4 tails, which are practically 100% conserved from yeast to mammals. The histone H3 and H4 tails are redundant in their essential function, as either one can be deleted in the presence of the other, but they cannot be deleted together. Moreover, the H3 and H4 tails can be interchanged to reside on the core of H4 and H3 respectively. Work from several laboratories have shown that H3 and H4 tails are important for proper gene regulation and DNA repair and it is proposed that this mechanism requires the posttranslational modification (methylation, acetylation, phosphorylation, etc.) of several key residues (lysines, arginine, serines and threonines) located within the tail of histones. The importance of each of these residues for specific functionalities of H3 and H4 tails is particularly difficult to investigate because of the functional redundancy within and between tails, and thus the elucidation of the link between specific residues and histone H3 and H4 tail functions would require a tremendous number of combinations of point mutations. To address these complex issues, my laboratory has set up a genetic screen taking advantage of the fact that simultaneous deletion in the N-terminal tails of H3 and H4 is unviable. A library of H3 molecules bearing N-terminal tails was designed with random sequences and screened for sequences that could restore viability in H3-H4 mutant strains. We successfully identified synthetic tails that restored not only viability, but also increased the fitness of the original strain in certain stress conditions. The current research program will thus focus on the characterization of these synthetic tails both biochemically and genetically to uncover their mechanisms of action. Such screening methods have proven to be extremely useful in identifying protein-protein interactions and understanding complex mechanisms.***In particular, we will focus on screening for H4 N-terminal tails as we have done with H3, and use proteomics and genetics approaches to find direct functional targets of these synthetic H3 and H4 histone tails. **