MAGNESIUM TRANSPORT IN SALMONELLA TYPHIMURIUM

本提案的长期目标是了解Mg 2+在 细胞生理学 Mg 2+是迄今为止最丰富的细胞内 二价阳离子，其细胞内浓度受到严格控制， 是细胞结构组件完整性所必需的， 这是许多重要代谢酶活性所必需的。 此外，委员会认为， 该实验室和其他实验室最近的工作表明，Mg 2+的作用 在原核和真核细胞中的基本调节作用。 它 因此，似乎所有的细胞都具有有趣的机制， 传感和控制Mg 2+通过电池的进入和离开 膜的 初步数据显示，存在三种 基因座（corA、mgtA和mgtB），这些基因座似乎 代表三种不同的Mg 2+转运系统。 至少两个其他基因座， corB和corC与CorA的转运相互作用 系统 MgtA和MgtB系统的运输受 细胞外Mg ~（2+）浓度。 鼠伤寒。 个别运输系统的特点将是 在仅携带一种功能性Mg 2+转运的突变株中测定 系统 目的对相关基因和基因产物进行分子生物学分析 通过对转运基因的测序， 鉴定和克隆，并确定起始位点， 转录终止。 目的II将扩展已经开始的Mg 2+转运的遗传分析， 寻找影响这三种基因中每一种功能的额外突变， 运输系统。 任何这样的新突变都将定位在 染色体，研究其表型特性，以及其分子生物学特性。 如目的I中所述测定的性质。 目的III将表征单个Mg 2+转运的性质 系统. 研究将包括调查a）阳离子特异性 和各体系阳离子迁移的动力学参数，B） 仅由CorA转运介导的Mg 2+流出特性 系统，c）每个运输系统的能源，使用抑制剂 在能量偶联缺陷的unc突变体中的研究，和d）lacZ 操纵子融合到mgtA和mgtB的启动子，以表征 Mg 2+对这些位点的调控现象。

The long term goal of this proposal is to understand the role of Mg2+ in cellular physiology. Mg2+ is by far the most abundant intracellular divalent cation, its intracellular concentration is tightly controlled, it is required for the integrity of cell structural components, and it is necessary for the activity of many important metabolic enzymes. Moreover, recent work from this and other laboratories has suggested that Mg2+ plays a fundamental regulatory role in prokaryotic and eukaryotic cells. It seems probable therefore that all cells possess interesting mechanisms for sensing and controlling the entry and exit of Mg2+ through the cell membrane. The preliminary data presented establish the existence of three loci (corA, mgtA, and mgtB) in Salmonella typhimurium which appear to represent three distinct mg2+ transport systems. At least two other loci, corB and corC, have been identified that interact with the CorA transport system. Transport by the MgtA and MgtB systems is regulated by the extracellular concentration of Mg2+ across the cell membrane in S. typhimurium. Characteristics of individual transport systems will be determined in mutant strains carrying only one functional Mg2+ transport system. Aim I proposes a molecular analysis of the genes and gene products involved in Mg2+ transport through sequencing of the transport genes already identified and cloned and the determination of the sites of initiation and termination of transcription. Aim II will extend the genetic analysis of Mg2+ transport already begun by seeking additional mutations that affect function of each of the three transport systems. Any such new mutations will be localized on the chromosome, their phenotypic properties investigated, and their molecular properties determined as described in Aim I. Aim III will characterize the properties of the individual Mg2+ transport systems. Studies will include investigation of a) the cation specificity and kinetic parameters of cation transport of each system, b) the properties of Mg2+ efflux which is mediated solely by the CorA transport system, c) the source of energy for each transport system, using inhibitor studies in unc mutants which defective in energy coupling, and d) lacZ operon fusions to the promoters of mgtA and mgtB to characterize the phenomenology of Mg2+ regulation of these loci.