Tian G, Maas W K
Department of Microbiology, New York University Medical Center, New York 10016.
Mol Microbiol. 1994 Aug;13(4):599-608. doi: 10.1111/j.1365-2958.1994.tb00454.x.
Arginine biosynthesis in Escherichia coli is negatively regulated by a hexameric repressor protein, encoded by the gene argR and the corepressor arginine. By hydroxylamine mutagenesis two types of argR mutants were isolated and mapped. The first type is transdominant. In heterodiploids, these mutant polypeptides reduce the activity of the wild-type repressor, presumably by forming heteropolymers. Four mutant repressor proteins were purified. Two of these map in the N-terminal half of the protein. Gel retardation experiments showed that they bind poorly to DNA, but they could be precipitated by L-arginine at the same concentration as the wild-type repressor. The other two mutant repressors map in the C-terminal half of the protein. They are poorly precipitated by L-arginine and they bind poorly to DNA. In addition, one of these mutants appears to exist as a dimer. The second type of argR mutant repressor consists of super-repressors. Such mutants behave as arginine auxotrophs as a result of hyper-repression of arginine biosynthetic enzymes. They map at many locations throughout the argR gene. Three arginine super-repressor proteins were purified. In comparison with the wild-type repressor, two of them were shown to have a higher DNA-binding affinity in the absence of bound arginine, while the third was shown to have a higher DNA-binding affinity when bound to arginine.
大肠杆菌中的精氨酸生物合成受到一种六聚体阻遏蛋白的负调控，该蛋白由基因argR编码，共阻遏物为精氨酸。通过羟胺诱变，分离并定位了两种类型的argR突变体。第一种类型是反式显性的。在异源二倍体中，这些突变多肽会降低野生型阻遏物的活性，可能是通过形成异源聚合物来实现的。纯化了四种突变阻遏蛋白。其中两种位于该蛋白的N端一半区域。凝胶阻滞实验表明，它们与DNA的结合能力较差，但它们能被与野生型阻遏物相同浓度的L-精氨酸沉淀。另外两种突变阻遏蛋白位于该蛋白的C端一半区域。它们很难被L-精氨酸沉淀，并且与DNA的结合能力也很差。此外，其中一种突变体似乎以二聚体形式存在。第二种类型的argR突变阻遏物由超级阻遏物组成。由于精氨酸生物合成酶的过度阻遏，这类突变体表现为精氨酸营养缺陷型。它们分布在整个argR基因的许多位置。纯化了三种精氨酸超级阻遏蛋白。与野生型阻遏物相比，其中两种在没有结合精氨酸时显示出更高的DNA结合亲和力，而第三种在与精氨酸结合时显示出更高的DNA结合亲和力。
