Nuclear Organization of RNA Polymerase III Transcription

描述(申请人提供)：遗传信息通常以染色体上的线性阵列表示，然而核DNA以高度紧凑的形式存在，其中对单个基因的访问必须被视为一个三维问题。一些真核生物中有限数量的基因座的细胞学证据表明，至少某些基因的定位与基因的转录活性有关，并且这种定位可以随着代谢和发育信号的变化而改变。使用萌芽酵母酿酒酵母，我们最近发现，275个tRNA基因，虽然广泛分布在线性基因组中，但在整个细胞周期中都聚集在核仁附近。这种tRNA基因的聚集，虽然在RNA聚合酶III(PolIII)转录调控和有序的前tRNA加工途径方面具有潜在的优势，但对酵母基因组的大部分空间组织具有显著的意义。这种聚集是PolIII转录依赖的，影响tRNA基因之间的重组和RNA聚合酶II的邻近转录。在初步研究中，我们现在已经证明，核仁tRNA基因的定位是一个两步过程，tRNA基因的凝集素依赖的聚集可以与微管依赖的簇到核仁的定位分开。这个项目的近期目标是描述酵母中单个tRNA基因的这种大规模组织的机制，以利用分子遗传学工具。 从长远来看，我们还将调查这种现象是否会影响哺乳动物中RNA聚合酶III转录单位的行为。人类和其他脊椎动物的基因组不仅包含数百个tRNA基因，还包含数十万个带有tRNA类启动子的短DNA元件(Sine)。已知其中一些短的散布DNA元件(Sine)既影响RNA聚合酶II的附近转录，也影响与发育异常和癌症相关的重组事件。我们预计，了解PolIII转录单位的空间行为可以为限制基因组组织和调控提供更广泛的见解。与公共卫生相关：活细胞中的DNA极其浓缩，并以高度有组织的方式包装。这种包装有助于受监管的遗传信息检索，并影响可能导致癌症和发育异常的DNA重组事件。我们已经确定了一种丰富的DNA元件，分布在高等细胞的基因组中，既编码小RNA，又作为三维组织信号。我们正在研究这种组织的分子机制以及由此产生的DNA包装的性质。

DESCRIPTION (provided by applicant): Genetic information is usually represented as linear arrays on chromosomes, yet nuclear DNA exists in a highly compacted form in which access to individual genes must be considered as a three-dimensional problem. Cytological evidence for a limited number of loci in several eukaryotes has suggested that localization of at least some genes is related to the transcriptional activity of the genes, and that this positioning can change in response to metabolic and developmental signals. Using the budding yeast, Saccharomyces cerevisiae, we have recently shown that the 275 tRNA genes, although widely scattered in the linear genome, are gathered near the nucleolus throughout the cell cycle. This clustering of the tRNA genes, while potentially advantageous in terms of RNA polymerase III (pol III) transcriptional regulation and an ordered pre-Trna processing pathway, has striking implications for spatial organization of much of the yeast genome. The clustering is pol III transcription-dependent, and affects both recombinations between tRNA genes and nearby transcription by RNA polymerase II. In preliminary studies we have now shown that nucleolar tRNA gene localization is a two step process, with condensin-dependent clustering of the tRNA genes separable from microtubule-dependent localization of the clusters to the nucleolus. The near-term goal of this project is to characterize the mechanisms of this large-scale organization of the individual tRNA genes in yeast, to take advantage of the molecular genetic tools. In the longer term we will also investigate whether this phenomenon affects the behavior of RNA polymerase III transcription units in mammals. Genomes from humans and other vertebrates contain not only hundreds of tRNA genes, but hundreds of thousands of short interspersed DNA elements (SINEs) with tRNA-class promoters. Some of these short interspersed DNA elements (SINEs) are known to influence both nearby transcription by RNA polymerase II and recombination events that are associated with developmental abnormalities and cancers. We anticipate that understanding the spatial behavior of pol III transcription units could provide broad insights into constraints on genome organization and regulation. PUBLIC HEALTH RELEVANCE: DNA in living cells is extremely condensed and packaged in a highly organized fashion. This packaging facilitates regulated retrieval of genetic information and affects DNA recombination events that can lead to cancers and developmental abnormalities. We have identified a type of abundant DNA element, distributed throughout genomes of higher cells, that both encodes small RNAs and serves as a three-dimensional organization signal. We are investigating the molecular mechanisms of this organization and the nature of the resulting DNA packaging.