CHARACTERIZATION OF MALT MUTANTS THAT CONSTITUTIVELY ACTIVATE THE MALTOSE REGULON OF ESCHERICHIA-COLI
CHARACTERIZATION OF MALT MUTANTS THAT CONSTITUTIVELY ACTIVATE THE MALTOSE REGULON OF ESCHERICHIA-COLI
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DOI：
10.1128/jb.172.4.1846-1852.1990
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发表时间：
1990-04-01
影响因子：
3.2
通讯作者：
RAIBAUD, O
中科院分区：
文献类型：
--
作者：
DARDONVILLE, B;RAIBAUD, O
大肠杆菌的麦芽糖调控基因的表达受一种转录激活因子（malT基因的产物）的控制，并由生长培养基中麦芽糖或麦芽糖糊精的存在诱导。我们分离了8个突变体，这些突变体在malT中导致了该调控子的组成性表达。突变基因的核苷酸序列显示，这8个突变集中在malT基因前三分之一的两个小区域。纯化了两个突变的MalT蛋白（对应于每个簇中的突变），并检测了MalT依赖性malPp启动子的体外激活。而野生型MalT的活性完全依赖于麦芽糖的存在，即使在高浓度的蛋白质中，两种突变蛋白在没有这种糖的情况下也有部分活性。事实上，虽然在低蛋白浓度下，突变蛋白的活性仍然被麦芽糖糖增加，但在高浓度下，没有麦芽糖糖的情况下，这些蛋白完全活跃。两种蛋白对麦芽糖的亲和力都比野生型蛋白高5倍。
The expression of the maltose regulon of Escherichia coli is controlled by a transcriptional activator, the product of the malT gene, and is induced by the presence of maltose or maltodextrins in the growth medium. We isolated eight mutants with mutations in malT which lead to constitutive expression of the regulon. The nucleotide sequences of the mutated genes revealed that the eight mutations are clustered in two small regions in the first one-third of the malT gene. Two mutated MalT proteins (corresponding to a mutation in each cluster) were purified and examined for in vitro activation of the MalT-dependent malPp promoter. Whereas wild-type MalT activity was absolutely dependent upon the presence of maltatriose, even at high protein concentrations, both mutated proteins were partially active in the absence of this sugar. Indeed, while the activity of the mutated proteins was still increased by maltotriose at low protein concentrations, the proteins were fully active in the absence of maltotriose at high concentrations. Both proteins exhibited a fivefold-higher affinity for maltotriose than the wild-type protein did.