GENETIC CONTROL OF HEME SYNTHESIS IN S. TYPHIMURIUM

鼠伤寒沙门氏菌血红素合成的基因控制

• 批准号: 3297892
• 负责人: THOMAS EDWARD ELLIOTT
• 金额: $ 9.9万
• 依托单位: UNIVERSITY OF ALABAMA AT BIRMINGHAM
• 依托单位国家: 美国
• 财政年份: 1988
• 资助国家: 美国
• 起止时间: 1988-07-01 至 1993-12-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/3297892
• 关键词: 5 aminolevulinate synthase; Salmonella typhimurium; anaerobiosis; bacterial genetics; chimeric proteins; electron transport; enteric bacteria; enzyme mechanism; fermentation; gene expression; genetic mapping; genetic promoter element; genetic regulation; genetic regulatory element; heme; immunoprecipitation; lac operon; microorganism metabolism; molecular cloning; mutant; nucleic acid sequence; porphyrin biosynthesis; radiotracer; starvation; superoxide dismutase

Heme serves Salmonella typhimurium as the cofactor both for cytochromes (required for respiration) and for catalase (involved in defense against oxygen's toxic effects). In S. typhimurium, the heme pathway also leads to siroheme and to vitamin B 12, which is an essential nutrient for humans. Surprisingly, very little is known about the regulation of this branched pathway in enteric bacteria. Since S. typhimurium well-suited to genetic analysis, we propose a primarily genetic approach to understanding the control of heme synthesis. We have been investigating the role of the hemA and hemL genes in the synthesis of ALA, the first committed, stable intermediate in the heme pathway. We have also identified a large number of hem mutants, and characterized the genes so defined. Here we concentrate on three specific systems chosen to illuminate different aspects of heme regulation. The hemA gene encodes the first enzyme specific to the heme pathway, glutamyl tRNA reductase. We are studying control of hemA gene expression during starvation for heme and in different growth conditions. We've also discovered a pair of genes, hemF and hemN, that encode alternative aerobic and anaerobic enzymes for a late step in heme synthesis, and we'll study the influence of oxygen on these genes. Finally, we've learned that S. typhimurium has two routes of ALA synthesis, and we suspect that this duality is important in regulating flow through the pathway to different end products. This study is also relevant to the larger problem of S. typhimurium's life in the colon. Most of what we know about enteric bacteria has been observed during growth in air. As a facultative anaerobe, S. typhimurium respires to electron acceptors when they are present, but can also grow by fermentation in their absence. In nature, electron acceptors may be present only intermittently (in the diet, or as oxygen diffusing from the epithelial surface). The ability for rapid development of respiratory capacity may be very important. We'll attempt to exploit heme regulation as an approach to more general questions about control of gene function by oxygen.

血红素作为鼠伤寒沙门氏菌的辅因子，两者都是细胞色素 (呼吸所需)和过氧化氢酶(参与防御 氧气的毒性作用)。在鼠伤寒沙门氏菌中，血红素途径也导致 和维生素B12，这是人类的一种基本营养素。 令人惊讶的是，人们对这种分支的调节知之甚少。 肠道细菌中的途径。由于鼠伤寒沙门氏菌非常适合遗传 分析，我们提出了一个主要的遗传学方法来理解 血红素合成的控制。 我们一直在研究HEMA和HEML基因在 血红素中第一个稳定的中间体丙氨酸的合成 路径。我们还鉴定了大量的HEM突变体，以及 描述了如此定义的基因的特征。在这里，我们集中讨论三个具体问题 选择用于阐明血红素调节的不同方面的系统。这个 HEMA基因编码第一种专属于血红素途径的酶--谷氨酰基 TRNA还原酶。我们正在研究HEMA基因表达的控制 饥饿对血红素和不同生长条件的影响。我们也已经 发现了一对基因，hemF和hemn，它们编码交替的有氧 和厌氧酶在血红素合成的后期阶段，我们将研究 氧气对这些基因的影响。最后，我们了解到S。 鼠伤寒沙门氏菌有两条合成ALA的途径，我们怀疑 二元性在通过不同途径调节流量方面很重要。 最终产品。 这项研究也与鼠伤寒沙门氏菌的生命这一更大的问题有关 在结肠里。我们所知道的关于肠道细菌的大部分是 在空气中生长过程中观察到的。鼠伤寒沙门氏菌为兼性厌氧菌 当电子受体存在时，呼吸作用于它们，但也可以通过 在他们不在的情况下发酵。在自然界中，电子受体可能是 仅间歇性存在(在饮食中，或作为氧气从 上皮面)。呼吸系统的快速发育能力 容量可能非常重要。我们将尝试利用血红素的调节 作为解决有关基因功能控制的更一般问题的一种方法 氧气。