GENETIC CONTROL OF HEME SYNTHESIS IN S. TYPHIMURIUM

血红素作为鼠伤寒沙门氏菌的辅助因子 细胞色素(呼吸所需)、过氧化氢酶和 超氧化物歧化酶(参与防御氧的毒性 效果)。在沙门氏菌中，血红素途径也会导致西罗西莫症。 还有维生素B12，这是人类必不可少的营养物质。 令人惊讶的是，人们对此的监管知之甚少。 肠道细菌中的分支途径。因为沙门氏菌很好- 适合于遗传分析，我们提出了一个主要的遗传 理解血红素合成控制的方法。 这项研究也与沙门氏菌的更大问题有关 结肠里的生活。我们对肠道细菌的大部分了解 在空气中生长的过程中被观察到。作为兼容词 厌氧菌，沙门氏菌当它们被电子受体呼吸时 现在存在，但也可以在没有它们的情况下通过发酵生长。在……里面 自然，电子受体可能只间歇性地存在(在 饮食，或作为氧气从上皮表面扩散)。这个 快速发展呼吸能力的能力可能会很强 很重要。我们将尝试利用血红素法规作为一种 关于基因功能调控的更一般问题的探讨 通过氧气 我们的初步研究集中在这条途径的第一步， 丙氨酸的合成。我们了解到沙门氏菌有两条途径 ，我们怀疑这种二元性在 调节流向不同最终产品的途径。 丙氨酸合成的主要途径(包括好氧合成和 厌氧)取决于hemeA和hem1基因。我们会 描述这些基因及其调控，并研究 酶，丙氨酸合成酶。丙氨酸的第二条合成路线是 仅在厌氧状态下表达。这可能与C5路线有关 用于光合作用有机体的丙氨酸合成。我们已经 分离的与大多数血红素基因的泥胶融合 途径，我们将使用这些选择和表征突变 调节血红素基因的表达。有一套井 特色化的em突变体和使用的简单方法 它们还可以快速进行分子生物学表征 这些基因和亚铁血红素途径酶。

Heme serves Salmonella typhimurium as the cofactor both for cytochromes (required for respiration) and for catalase and superoxide dismutase (involved in defense against oxygen's toxic effects). In Salmonella, the heme pathway also leads to siroheme and to vitamin B12, which is an essential nutrient for humans. Surprisingly, very little is known about the regulation of this branched pathway in enteric bacteria. Since Salmonella is well- suited to genetic analysis, we propose a primarily genetic approach to understanding the control of heme synthesis. This study is also relevant to the larger problem of Salmonella's life in the colon. Most of what we know about enteric bacteria has been observed during growth in air. As a facultative anaerobe, Salmonella 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 Our initial studies have focused on the first step of the pathway, synthesis of ALA. We've learned that Salmonella has two routes of ALA synthesis, and we suspect that this duality is important in regulating flow through the pathway to different end products. The major route of ALA synthesis (both aerobically and anaerobically) depends on the hemeA and hemL genes. We'll characterize these genes and their regulation, and study the enzyme, ALA synthase. The second route of ALA synthesis is expressed only anaerobically. It may be related to the C5 route of ALA synthesis used in photosynthetic organisms. We've isolated Mud-lac fusions to most of the genes of the heme pathway, and we'll use these select and characterize mutations regulating expression of heme genes. Having a set of well characterized hem mutants and simple methods for working with them also allow rapid molecular biological characterization of these genes and the heme pathway enzymes.