GENETIC CONTROL OF HEME SYNTHESIS IN S. TYPHIMURIUM

血红素作为鼠伤寒沙门氏菌的辅因子， 细胞色素（呼吸所需）和过氧化氢酶， 超氧化物歧化酶（参与防御氧气的毒性 效果）。 在沙门氏菌中，血红素途径也导致siroheme 以及维生素B12，这是人类必需的营养素。 令人惊讶的是，很少有人知道这方面的规定， 肠道细菌中的分支途径。 因为沙门氏菌- 适合遗传分析，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。 结肠中的生命 我们对肠道细菌的了解 在空气中生长时观察到。 作为一个临时的 沙门氏菌在厌氧条件下， 存在，但也可以通过发酵生长在他们的缺席。 在 在自然界中，电子受体可以仅间歇性地存在（在 饮食，或作为从上皮表面扩散的氧）。 的 快速发展呼吸能力的能力可能非常 重要. 我们将尝试利用血红素调节作为 关于基因功能控制的更一般性问题的探讨 被氧 我们最初的研究集中在途径的第一步， ALA的合成。 我们知道沙门氏菌有两条途径 ALA合成，我们怀疑这种二元性是重要的， 调节通过所述通路到不同终产物的流动。 ALA合成的主要途径（有氧和有氧） 厌氧条件下）依赖于hemeA和hemL基因。 我们会 描述这些基因及其调控，并研究 酶，ALA合成酶。 ALA合成的第二条路线是 仅在厌氧条件下表达。 可能与C5路线有关 ALA合成的最新进展。 我们 分离的Mud-lac融合到血红素的大部分基因， 我们将使用这些选择和特征化的突变 调节血红素基因的表达。 有一套井 表征的hem突变体和使用hem突变体的简单方法 它们还允许快速的分子生物学表征， 这些基因和血红素途径酶。

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.