GENETIC CONTROL OF NITRATE RESPIRATION IN E COLI

肠道细菌有效地调节它们的呼吸代谢 对诸如氧的替代电子受体的可用性的响应， 硝酸盐和富马酸。这一规定的协调是为了确保使用 最有效的呼吸途径。在没有氧气、硝酸盐、 首选厌氧电子受体，诱导合成酶 硝酸盐呼吸(甲酸脱氢酶-N和硝酸还原酶) 抑制其他厌氧呼吸酶的合成，如 富马酸还原酶。该项目的长期目标是了解 硝酸盐协调的生理和遗传机制 以不同的方式调节不同厌氧途径的合成。 以前的工作已经确定了两个基因，narL和narX，这是必需的 用于硝酸盐诱导硝酸还原酶的合成和硝酸盐的抑制 富马酸还原酶的合成。NarL基因产物NARL是 被认为是一种DNA结合蛋白，调节转录 对硝酸盐的反应。NarX基因产物，NARX，被假设为 将NARL转换为其抑制器形式。NARL和NARX显示序列相似性 到SIGNAL涉及的“双组分监管体系” 转导。 该项目将通过以下方式定义narL和narX在调节中的角色 分离和鉴定这些基因中的功能突变，方法是 NarL和NarX在不同生长条件下的相互独立表达 条件，并通过分析NARL与其目标DNA位点的结合。这个 NarL复合操纵子的结构和表达将通过 操纵子和基因融合以及转录图谱，以便理解 NarX和narL的表达调控。将进行搜索以寻找 假设基因“narQ”，可能需要将NARL转化为 它的激活剂形式。最后，甲酸盐的结构基因 脱氢酶-N将被鉴定，它们被硝酸盐和 NARL将通过遗传和分子生物学方法进行分析。 总而言之，这些研究将提供关于硝酸盐如何 调节和协调无氧代谢。

Enterobacteria efficiently regulate their respiratory metabolism in response to availability of alternate electron acceptors such as oxygen, nitrate and fumarate. This regulation is coordinated to ensure use of the most efficient respiratory pathway. In the absence of oxygen, nitrate, the preferred anaerobic electron acceptor, induces synthesis of enzymes for nitrate respiration (formate dehydrogenase-N and nitrate reductase) while repressing the synthesis of other anaerobic respiratory enzymes such as fumarate reductase. The long-term goals of this project are to understand the physiological and genetic mechanisms by which nitrate coordinately regulates the synthesis of different anaerobic pathways in different ways. Previous work has identified two genes, narL and narX, which are required for nitrate induction of nitrate reductase synthesis and nitrate repression of fumarate reductase synthesis. The narL gene product, NARL, is hypothesized to be a DNA-binding protein that regulates transcription in response to nitrate. The narX gene product, NARX, is hypothesized to convert NARL to its repressor form. NARL and NARX show sequence similarity to the group of "two-component regulatory systems" involved in signal transduction. This project will define the roles of narL and narX in regulation by isolating and characterizing altered function mutations in these genes, by expressing narL and narX independently of each other under various growth conditions, and by analyzing binding of NARL to its target DNA sites. The structure and expression of the narL complex operon will be analyzed by operon and gene fusions and by transcript mapping, in order to understand the regulation of narX and narL expression. A search will be made for a hypothetical gene, "narQ", that may be required for conversion of NARL to its activator form. Finally, the structural genes for formate dehydrogenase-N will be identified, and their regulation by nitrate and NARL will be analyzed by genetic and molecular biological methods. Together, these studies will provide a more detailed view of how nitrate regulates and coordinates anaerobic metabolism.