Margelis S, D'Souza C, Small A J, Hynes M J, Adams T H, Davis M A
Department of Genetics, The University of Melbourne, Parkville, Victoria, 3010, Australia.
J Bacteriol. 2001 Oct;183(20):5826-33. doi: 10.1128/JB.183.20.5826-5833.2001.
Glutamine synthetase (GS), EC 6.3.1.2, is a central enzyme in the assimilation of nitrogen and the biosynthesis of glutamine. We have isolated the Aspergillus nidulans glnA gene encoding GS and have shown that glnA encodes a highly expressed but not highly regulated mRNA. Inactivation of glnA results in an absolute glutamine requirement, indicating that GS is responsible for the synthesis of this essential amino acid. Even when supplemented with high levels of glutamine, strains lacking a functional glnA gene have an inhibited morphology, and a wide range of compounds have been shown to interfere with repair of the glutamine auxotrophy. Heterologous expression of the prokaryotic Anabaena glnA gene from the A. nidulans alcA promoter allowed full complementation of the A. nidulans glnADelta mutation. However, the A. nidulans fluG gene, which encodes a protein with similarity to prokaryotic GS, did not replace A. nidulans glnA function when similarly expressed. Our studies with the glnADelta mutant confirm that glutamine, and not GS, is the key effector of nitrogen metabolite repression. Additionally, ammonium and its immediate product glutamate may also act directly to signal nitrogen sufficiency.
谷氨酰胺合成酶（GS），酶编号为EC 6.3.1.2，是氮同化和谷氨酰胺生物合成中的关键酶。我们已经分离出了构巢曲霉中编码GS的glnA基因，并表明glnA编码一种高表达但调控程度不高的mRNA。glnA的失活导致对谷氨酰胺的绝对需求，这表明GS负责这种必需氨基酸的合成。即使补充高水平的谷氨酰胺，缺乏功能性glnA基因的菌株仍具有受抑制的形态，并且已证明多种化合物会干扰谷氨酰胺营养缺陷型的修复。来自构巢曲霉alcA启动子的原核鱼腥藻glnA基因的异源表达能够完全互补构巢曲霉glnAΔ突变。然而，构巢曲霉中编码与原核GS相似蛋白质的fluG基因，在类似表达时并不能替代构巢曲霉glnA的功能。我们对glnAΔ突变体的研究证实，谷氨酰胺而非GS是氮代谢物阻遏的关键效应物。此外，铵及其直接产物谷氨酸也可能直接作用以信号氮充足。
