Crosstalk between DNA repair pathways in repeat instability

项目总结/摘要 大约一半的人类基因组是由重复的DNA序列组成的，这些序列被认为控制着一个基因组。 广泛的细胞功能。DNA重复序列存在于整个基因组中，并且在长度上具有多态性 因为他们的基因不稳定。重复元件的突变率是其他部分的101-105倍。 基因组，并触发形成短暂的不寻常的DNA结构（螺旋外挤出） 在DNA代谢过程中。重复不稳定性的有害后果由三重态 导致许多神经退行性疾病如亨廷顿病的重复扩张， 弗里德赖希共济失调和脆性X相关疾病。三联体重复序列的扩增速率与 重复长度和序列均一性。DNA修复机制已经进化到维持基因组稳定性， 并保护DNA免受环境因素的损害。其中一个过程是DNA错配修复 (MMR)，一种高度保守的抗突变途径，通过以下方式维持人类基因组的稳定性： 纠正复制错误和防止染色体重排。出乎意料的是，一种诱变的非- MMR的典型功能被认为是三联体重复扩增的原因。MMR功能丧失 减弱三联体重复扩增，尽管这种非典型MMR活性的分子机制是 不太了解。然而，MMR的这种致突变作用需要蛋白MutSb和MutLa（以及可能的 MutLg）。FAN 1是一种脱氧核糖核酸酶，最初被鉴定为参与DNA修复的因子 股间交联。FAN 1功能的丧失加剧了重复扩增，表明FAN 1在 通过尚不清楚的机制抑制三联体重复扩增。我们感兴趣的是 分子机制负责MMR和FAN 1的这些相反效应之间的串扰， 控制三联体重复内的突变产生。我们发现了一种新的FAN 1核酸酶激活剂 这一发现不仅代表了我们对这一机制的理解， FAN 1作用的研究，也有助于我们对三联体重复序列的机制有一个统一的认识。 通过整合生化、细胞和遗传研究进行扩展。在目标1中，我们将阐明分子 通过评估DNA序列/结构和蛋白质的调节作用来表征FAN 1核酸酶功能 辅因子在目标2中，我们将剖析蛋白质-DNA和蛋白质-蛋白质相互作用在三联体修复中的作用。 通过FAN 1重复挤出。在目标3中，我们将使用无偏的蛋白质组学方法来鉴定辅助因子， 促进FAN 1核酸酶在细胞环境中的功能。这些研究的完成将有助于了解 调节三联体重复扩增，并将对基因组的机制产生更广泛的影响。 不稳定

Project Summary/Abstract Approximately half the human genome is comprised of repetitive DNA sequences that are thought to control a wide range of cellular functions. DNA repeats are found throughout the genome, and are polymorphic in length due to their genetic instability. Mutation rates of repeat elements are 101-105 fold higher than in other parts of the genome, and is triggered by the formation of transient unusual DNA structures (extrahelical extrusions) during DNA metabolic processes. The detrimental consequences of repeat instability are exemplified by triplet repeat expansions that cause a number of neurodegenerative diseases such as Huntington’s disease, Friedreich’s ataxia and Fragile X related disorders. The rate of expansion of triplet repeats is proportional to repeat length and sequence homogeneity. DNA repair mechanisms have evolved to maintain genomic stability, and protect the DNA from damage caused by environmental agents. One such process is DNA mismatch repair (MMR), a highly conserved antimutagenic pathway that maintains the stability of the human genome by correcting replication errors and preventing chromosomal rearrangements. Unexpectedly, a mutagenic non- canonical function of MMR has been implicated as the cause of triplet repeat expansions. Loss of MMR function attenuates triplet repeat expansion, although the molecular mechanisms of this non-canonical MMR activity are poorly understood. However, this mutagenic action of MMR requires the proteins MutSb and MutLa (and possibly MutLg). FAN1 is a deoxyribonuclease that was originally identified as a factor involved in the repair of DNA interstrand crosslinks. Loss of FAN1 function exacerbates repeat expansion, suggesting a role for FAN1 in suppression of triplet repeat expansion by mechanisms that are not understood. We are interested in the molecular mechanisms responsible for the crosstalk between these opposing effects of MMR and FAN1 in the control of mutation production within triplet repeats. We have discovered a novel activator of the FAN1 nuclease on triplet repeat extrusions, a finding that represents the first step not only in our understanding of the mechanism of FAN1 action, but also in our quest to develop a unified understanding of the mechanism of triplet repeat expansion by integrating biochemical, cellular, and genetic studies. In Aim 1, we will elucidate the molecular features of FAN1 nuclease function by evaluating the modulatory effects of DNA sequence/structure and protein co-factors. In Aim 2, we will dissect the role of protein-DNA and protein-protein interactions in the repair of triplet repeat extrusions by FAN1. In Aim 3, we will use unbiased proteomic approaches to identify co-factors that facilitate FAN1 nuclease function in a cellular milieu. Completion of these studies will shed light on the pathways that modulate triplet repeat expansion, and will have implications more broadly for the mechanisms of genome instability.