Meiotic Interactions of the RecA Homologue Dmc1

描述(申请人提供)：同源重组在减数分裂中染色体的减少分离中起关键作用。减数分裂重组是由程序性诱导DNA双链断裂(DSB)启动的，涉及有丝分裂细胞中DSB的重组修复机制。减数分裂和有丝分裂重组的关键区别在于减数分裂过程必须发生在同源染色单体之间，而有丝分裂过程通常发生在姐妹染色单体之间。重组的中心步骤是同源链的入侵和交换。这一过程是由重组酶催化的，重组酶在结构和功能上与细菌链交换蛋白RecA相关。大多数真核生物，包括发芽酵母和人类，都存在两种RecA样重组酶；RAD51是唯一参与有丝分裂重组的RecA样重组酶。Dmc1是一种减数分裂特异性重组酶，可以在缺少RAD51的情况下发挥作用，但通常与RAD51协同工作。为了促进链侵袭，重组酶必须首先在DSB位点形成的单链DNA(SsDNA)束上聚合成螺旋丝。被称为介体的辅助因子允许重组酶在单链DNA结合蛋白形成细丝时取代它们。最近的证据表明，第二种类型的辅助因子消耗能量来促进重组酶从DMA解离。这项拟议的工作旨在阐明萌芽酵母中的减数分裂重组。本研究的目的是：1.确定重组酶激活型ATPase Tid1/Rdh54和Rad54在体内的功能。2.确定DmCL的辅助因子刺激其生化活性的机制。3.为了检验一个模型的预测，在该模型中，Dmcvs支持同源染色单体之间的重组而不是姐妹染色单体之间的重组的能力反映了它形成的细丝的刚性以及这些细丝距离轴向元件的距离。4.通过定位5个dmc1-ts抑制基因和分离绕过辅助因子要求的DMC1的等位基因，从遗传学上表征DMC1的相互作用。减数分裂重组的缺陷会导致染色体不分离和丢失，从而导致出生缺陷和自然流产。有丝分裂中重组修复的失败与乳腺癌和其他恶性肿瘤的病因有关。

DESCRIPTION (provided by applicant): Homologous recombination plays a critical role in reductional segregation of chromosomes in meiosis. Meiotic recombination is initiated by the programmed induction of DNA double strand breaks (DSBs) and involves a mechanism related to recombinational repair of DSBs in mitotic cells. The key difference between meiotic and mitotic recombination is that the meiotic process must occur between homologous chromatids and the mitotic process usually occurs between sister chromatids. The central step of recombination is homologous strand invasion and exchange. This process is catalyzed by recombinases that are structurally and functionally related to the bacterial strand exchange protein, RecA. There are two RecA-like recombinases in most eukaryotic organisms, including budding yeast and humans; Rad51 is the only RecA- like recombinase involved in mitotic recombination. Dmc1 is a meiosis-specific recombinase that can function in the absence of Rad51, but often cooperates with it. In order to promote strand invasion, recombinases must first polymerize into helical filaments on the tracts of single strand DMA (ssDNA) that form at sites of DSBs. Accessory factors, called mediators, allow recombinase to displace single strand DMA binding proteins as they form filaments. Recent evidence indicates that a second type of accessory factor expends energy to promote dissociation of recombinases from DMA. The proposed work seeks to elucidate meiotic recombination in budding yeast. The aims of this proposal are: 1. To determine the in vivo function of the recombinase-stimulating ATPases Tid1/Rdh54 and Rad54. 2. To determine the mechanisms through which Dmcl's accessory factors stimulate its biochemical activity. 3. To test predictions of a model in which DmcVs ability to favor recombination between homologous chromatids over that between sister chromatids reflects the rigidity of the filaments it forms and the distance these filaments project away from the axial element. 4. To characterize DMC1 interactions genetically by mapping 5 dmc1-ts suppressors and by isolating alleles of DMC1 that bypass accessory factor requirements. Defects in meiotic recombination cause chromosome non-disjunction and loss, both of which lead to birth defects and spontaneous abortion. Failure of recombinational repair in mitosis is implicated in the etiology of breast cancer and other malignancies.