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首页> 外文期刊>Journal of bacteriology >Alanine Catabolism in Klebsiella aerogenes: Molecular Characterization of the dadAB Operon and Its Regulation by the Nitrogen Assimilation Control Protein
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Alanine Catabolism in Klebsiella aerogenes: Molecular Characterization of the dadAB Operon and Its Regulation by the Nitrogen Assimilation Control Protein

机译：产气克雷伯菌中的丙氨酸分解代谢：dadAB操纵子的分子表征及其受氮同化控制蛋白的调节

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Klebsiella aerogenes strains with reduced levels ofd-amino acid dehydrogenase not only fail to use alanine as a growth substrate but also become sensitive to alanine in minimal media supplemented with glucose and ammonium. The inability of these mutant strains to catabolize the alanine provided in the medium interferes with both pathways of glutamate production. Alanine derepresses the nitrogen regulatory system (Ntr), which in turn represses glutamate dehydrogenase, one pathway of glutamate production. Alanine also inhibits the enzyme glutamine synthetase, the first enzyme in the other pathway of glutamate production. Therefore, in the presence of alanine, strains with mutations in dadA (the gene that codes for a subunit of the dehydrogenase) exhibit a glutamate auxotrophy when ammonium is the sole source of nitrogen. The alanine catabolic operon of Klebsiella aerogenes,dadAB, was cloned, and its DNA sequence was determined. The clone complemented the alanine defects of dadA strains. The operon has a high similarity to the dadAB operon ofSalmonella typhimurium and the dadAX operon ofEscherichia coli, each of which codes for the smaller subunit of d-amino acid dehydrogenase and the catabolic alanine racemase. Unlike the cases for E. coli and S. typhimurium, the dad operon of K. aerogenes is activated by the Ntr system, mediated in this case by the nitrogen assimilation control protein (NAC). A sequence matching the DNA consensus for NAC-binding sites is located centered at position ?44 with respect to the start of transcription. The promoter of this operon also contains consensus binding sites for the catabolite activator protein and the leucine-responsive regulatory protein.
机译：降低d-氨基酸脱氢酶水平的产气克雷伯氏菌不仅不能使用丙氨酸作为生长底物，而且在补充葡萄糖和铵的基本培养基中对丙氨酸敏感。这些突变菌株不能分解代谢培养基中提供的丙氨酸，这会干扰谷氨酸生产的两种途径。丙氨酸会抑制氮调节系统（Ntr），反过来会抑制谷氨酸脱氢酶，这是谷氨酸生产的一种途径。丙氨酸还抑制谷氨酰胺合成酶，这是谷氨酸生产另一种途径中的第一个酶。因此，在存在丙氨酸的情况下，当铵是唯一的氮源时，在 dadA （编码脱氢酶亚基的基因）中突变的菌株表现出谷氨酸营养缺陷型。克隆了产气单胞菌克雷伯菌， dadAB 的丙氨酸分解代谢操纵子，并确定了其DNA序列。该克隆弥补了 dadA 菌株的丙氨酸缺陷。该操纵子分别与鼠伤寒沙门氏菌的 dadAB 操纵子和大肠杆菌的 dadAX 操纵子具有高度相似性。其中编码d-氨基酸脱氢酶和分解代谢的丙氨酸消旋酶的较小亚基。与 E的情况不同。大肠菌和 S。 typhimurium ， K的 dad 操纵子。 Ntr系统激活了产气素，在这种情况下，它由氮同化控制蛋白（NAC）介导。相对于NAC结合位点，与DNA共有序列相匹配的序列位于相对于转录开始的位置α44的中心。该操纵子的启动子还包含分解代谢物激活蛋白和亮氨酸反应性调节蛋白的共有结合位点。

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