Characterization of structurally atypical sigma factors carrying fused domains of unknown function in the plant endosymbiont, Sinorhizobium meliloti

植物内共生体苜蓿中华根瘤菌中携带未知功能融合域的结构非典型西格玛因子的表征

• 批准号: RGPIN-2018-04583
• 负责人: Maclellan, Shawn
• 金额: $ 2.62万
• 依托单位: University of New Brunswick
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=686540
• 关键词: Characterization; structurally; atypical; sigma; factors

Transcription is the first major step in gene expression in all organisms. In bacteria, all gene expression is regulated by a family of general transcription factors called sigma () factors. Each factor controls the expression of a subset (its regulon) of genes and regulons may consist of between one and thousands of genes depending on the factor. An important group of these proteins is comprised of Extracytoplasmic Function (ECF) factors and the activity of many of these is negatively regulated by a signal transduction pathway that includes an antagonistic anti- factor protein. ECF factors and their associated regulators constitute a major sensory system that, along with specific transcription factors and two-component regulatory systems, mediate the cellular ability to mount appropriate gene expression responses to changing physicochemical conditions inside and outside of the cell. ******Mechanistically, factors carry out two major functions: they target RNAP holoenzyme to the gene promoter and they trap the transcription start site in a single-stranded state called an open-complex. Stabilization of the open-complex is an essential step in the transcription initiation pathway and factor activity is partially analogous to the activity of TFIIB in archaeal and eukaryotic RNAP II. Understanding mechanistic detail of factor function is a very active area of research that involves a few well-characterized model systems. However, the analysis of genome sequence data has revealed the presence of structurally unusual ECF factor-related proteins in many bacteria and these atypical or non-canonical systems remain understudied. Several sub-groups of ECF factors unexpectedly carry fused protein domains of unknown or incompletely characterized function. Emerging evidence points to regulatory functions for these fused domains and the long term objective of my research program is to study mechanistic details of non-canonical transcription systems in bacteria. The study of non-canonical systems carries the promise of uncovering novel pathways to transcription initiation and unexpected physiological relationships between the regulation of gene expression and other cellular processes.*** ***Remarkably, the important endosymbiotic bacterium Sinorhizobium meliloti synthesizes two unique examples of non-canonical fused domain factors. This current proposal describes the study of the physiological importance of one of these proteins (RpoE9) to S. meliloti biology. To these ends, we are proposing a series of research pursuits mainly focused on discerning unexpected intersections between RpoE9 activity and other cellular regulatory and homeostatic systems. We wish to emphasize that while the study of this structurally atypical factor is important in itself, we also view it as a vehicle to establish and refine the study of all ECF factors from a more global and systems-wide perspective. *****

转录是所有生物体基因表达的第一个主要步骤。在细菌中，所有基因的表达都受一系列被称为sigma()因子的通用转录因子的调节。每个因子控制基因的一个子集(其调节子)的表达，根据因子的不同，调节子可能由一个到数千个基因组成。其中一组重要的蛋白质由胞质外功能(ECF)因子组成，其中许多蛋白质的活性受到信号转导途径的负调控，其中包括一种拮抗的抗因子蛋白。ECF因子及其相关调节因子构成一个主要的感觉系统，与特定的转录因子和双组分调节系统一起，介导细胞对细胞内外不断变化的物理化学条件做出适当的基因表达反应的能力。*从机制上讲，因子有两个主要功能：它们针对基因启动子的RNAP全酶，它们以一种称为开放复合体的单链状态捕获转录起始点。开放复合体的稳定是转录起始途径中的重要步骤，因子活性与古生物和真核生物RNAP II中TFIIB的活性部分相似。了解因子功能的机制细节是一个非常活跃的研究领域，涉及到一些特征良好的模型系统。然而，对基因组序列数据的分析表明，许多细菌中存在结构不寻常的ECF因子相关蛋白，这些非典型或非规范系统仍未得到充分研究。几个ECF因子亚群出人意料地携带功能未知或功能不完全的融合蛋白结构域。新出现的证据表明，这些融合结构域具有调控功能，我的研究计划的长期目标是研究细菌中非规范转录系统的机制细节。对非规范系统的研究有望揭示转录起始的新途径，以及基因表达调控和其他细胞过程之间意想不到的生理关系。值得注意的是，重要的内共生细菌苜蓿中华根瘤菌合成了两个独特的非规范融合结构域因子。目前的建议描述了其中一种蛋白(RpoE9)对苜蓿链霉菌生物学的生理重要性的研究。为此，我们提出了一系列研究目标，主要集中在识别RpoE9活性与其他细胞调节和内平衡系统之间的意想不到的交叉。我们要强调的是，虽然对这一结构上非典型因素的研究本身很重要，但我们也将其视为从更全球性和全系统的角度建立和完善对所有ECF因素的研究的一种工具。*****