PHYSIOLOGICAL-STUDIES OF TRYPTOPHAN TRANSPORT AND TRYPTOPHANASE OPERON INDUCTION IN ESCHERICHIA-COLI
PHYSIOLOGICAL-STUDIES OF TRYPTOPHAN TRANSPORT AND TRYPTOPHANASE OPERON INDUCTION IN ESCHERICHIA-COLI
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DOI：
10.1128/jb.173.19.6009-6017.1991
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发表时间：
1991-10-01
影响因子：
3.2
通讯作者：
GOLLNICK, P
中科院分区：
文献类型：
--
作者：
YANOFSKY, C;HORN, V;GOLLNICK, P
大肠杆菌形成三种可以运输氨基酸色氨酸的渗透酶：Mtr，AroP和TnaB。 这些渗透酶的结构基因存在于不同的操纵子中，这些操纵子受到不同的调节机制的影响。 我们利用色氨酸诱导色氨酸酶（tna）操纵子的事实来推断色氨酸转运是如何受到生长培养基和突变的影响，这些突变使每个通透酶蛋白质发生突变。 在酸水解酪蛋白培养基中，通常需要高水平的色氨酸以获得最大的tna操纵子诱导。 高水平是必要的，因为大部分添加的色氨酸被色氨酸酶降解。 另一种被色氨酸酶切割不良的诱导剂1-甲基色氨酸在低浓度下对tna+菌株和tna突变体都有效诱导。 在酸水解酪蛋白培养基中，TnaB通透酶对于色氨酸摄取是最关键的;即，只有tnaB的突变减少了葡聚糖酶的诱导。 然而，当1-甲基色氨酸取代色氨酸作为该培养基中的诱导剂时，需要mtr和tnaB中的突变来防止最大诱导。 在该培养基中，AroP不有助于色氨酸摄取。 然而，在缺乏苯丙氨酸和酪氨酸的培养基中，AroP通透酶在色氨酸转运中是活跃的;在这些条件下，有必要将三种通透酶混合以消除tna操纵子诱导。 Mtr通透酶主要负责转运吲哚，吲哚是色氨酸酶作用产生的色氨酸降解产物。 TnaB通透酶对于以色氨酸作为唯一碳源的生长是必需的。 当将具有高水平色氨酸酶的细胞转移到不含色氨酸的生长培养基中时，色氨酸（trp）操纵子的表达升高。 这一观察结果表明，存在于这些细胞中的色氨酸酶降解了一些合成的色氨酸，从而产生了轻度的色氨酸缺乏症。 我们的研究在不同的生理条件下，色氨酸运输分配角色的三个渗透酶。
Escherichia coli forms three permeases that can transport the amino acid tryptophan: Mtr, AroP, and TnaB. The structural genes for these permeases reside in separate operons that are subject to different mechanisms of regulation. We have exploited the fact that the tryptophanase (tna) operon is induced by tryptophan to infer how tryptophan transport is influenced by the growth medium and by mutations that inactivate each of the permease proteins. In an acid-hydrolyzed casein medium, high levels of tryptophan are ordinarily required to obtain maximum tna operon induction. High levels are necessary because much of the added tryptophan is degraded by tryptophanase. An alternate inducer that is poorly cleaved by tryptophanase, 1-methyltryptophan, induces efficiently at low concentrations in both tna+ strains and tna mutants. In an acid-hydrolyzed casein medium, the TnaB permease is most critical for tryptophan uptake; i.e., only mutations in tnaB reduce tryptophanase induction. However, when 1-methyltryptophan replaces tryptophan as the inducer in this medium, mutations in both mtr and tnaB are required to prevent maximum induction. In this medium, AroP does not contribute to tryptophan uptake. However, in a medium lacking phenylalanine and tyrosine the AroP permease is active in tryptophan transport; under these conditions it is necessary to inactivate the three permeases to eliminate tna operon induction. The Mtr permease is principally responsible for transporting indole, the degradation product of tryptophan produced by tryptophanase action. The TnaB permease is essential for growth on tryptophan as the sole carbon source. When cells with high levels of tryptophanase are transferred to a tryptophan-free growth medium, the expression of the tryptophan (trp) operon is elevated. This observation suggests that the tryptophanase present in these cells degrades some of the synthesized tryptophan, thereby creating a mild tryptophan deficiency. Our studies assign roles to the three permeases in tryptophan transport under different physiological conditions.