Dormeyer Miriam, Lentes Sabine, Richts Björn, Heermann Ralf, Ischebeck Till, Commichau Fabian M
Department of General Microbiology, Institute of Microbiology and Genetics, Georg-August-Universität Göttingen, Göttingen, Germany.
Institut für Molekulare Physiologie, Mikrobiologie und Weinforschung, Johannes Gutenberg-Universität Mainz, Mainz, Germany.
Front Microbiol. 2019 Oct 9;10:2321. doi: 10.3389/fmicb.2019.02321. eCollection 2019.
The Gram-positive soil bacterium relies on the glutamine synthetase and the glutamate synthase for glutamate biosynthesis from ammonium and 2-oxoglutarate. During growth with the carbon source glucose, the LysR-type transcriptional regulator GltC activates the expression of the glutamate synthase genes. With excess of intracellular glutamate, the genes are not transcribed because the glutamate-degrading glutamate dehydrogenases (GDHs) inhibit GltC. Previous studies revealed that 2-oxoglutarate and glutamate stimulate the activator and repressor function, respectively, of GltC. Here, we have isolated GltC variants with enhanced activator or repressor function. The majority of the GltC variants with enhanced activator function differentially responded to the GDHs and to glutamate. The GltC variants with enhanced repressor function were still capable of activating the promoter in the absence of a GDH. Using promoter variants ( ) that are active independent of GltC, we show that the wild type GltC and the GltC variants with enhanced repressor function inactivate promoters in the presence of the native GDHs. These findings suggest that GltC may also act as a repressor of the genes We discuss a model combining previous models that were derived from and experiments.
革兰氏阳性土壤细菌依靠谷氨酰胺合成酶和谷氨酸合酶从铵和2-氧代戊二酸合成谷氨酸。在以碳源葡萄糖生长期间，LysR型转录调节因子GltC激活谷氨酸合酶基因的表达。当细胞内谷氨酸过量时，这些基因不转录，因为降解谷氨酸的谷氨酸脱氢酶（GDH）抑制GltC。先前的研究表明，2-氧代戊二酸和谷氨酸分别刺激GltC的激活剂和阻遏物功能。在这里，我们分离出了具有增强激活剂或阻遏物功能的GltC变体。大多数具有增强激活剂功能的GltC变体对GDH和谷氨酸有不同的反应。具有增强阻遏物功能的GltC变体在没有GDH的情况下仍能够激活启动子。使用独立于GltC而具有活性的启动子变体（ ），我们表明野生型GltC和具有增强阻遏物功能的GltC变体在天然GDH存在下使启动子失活。这些发现表明GltC也可能作为这些基因的阻遏物。我们讨论了一个结合先前从 和 实验得出的模型的模型。
