Makino K, Shinagawa H, Nakata A
J Mol Biol. 1985 Jul 20;184(2):231-40. doi: 10.1016/0022-2836(85)90376-6.
The phoR gene product functions as a negative regulator with excess of phosphate and as a positive regulator with limited phosphate for the phosphate-starvation-inducible pho regulon of Escherichia coli. We constructed recombinant plasmids that contain a phoR'-'lacZ fusion gene to study the regulation of phoR expression. The genetic and physiological regulation of phoR expression was found to be very similar to that of phoB, a positive regulatory gene for the pho regulon, and phoA, the structural gene for alkaline phosphatase, both of which are inducible by phosphate limitation. The synthesis of the PhoR protein became non-inducible when the phoB promoter upstream of phoR, was removed from the hybrid plasmid, or when a transcriptional terminator was inserted in the phoB structural gene, irrespective of phosphate concentration in the medium. The results suggest that phoB and phoR constitute a single operon whose promoter is located proximal to phoB. The same low level of the PhoR protein in the cell can function as a positive regulator with limited phosphate and as a negative regulator with excess phosphate for the phoB-phoR operon. These results suggest that the maximal level of the operon is induced as consequences of both the increase in the quantity of the PhoR protein and of functional change of the protein as a positive regulator, which are induced by phosphate limitation.
phoR基因产物在磷酸盐过量时作为负调节因子，而在磷酸盐有限时作为正调节因子，作用于大肠杆菌的磷酸盐饥饿诱导型pho操纵子。我们构建了含有phoR'-'lacZ融合基因的重组质粒，以研究phoR表达的调控。结果发现，phoR表达的遗传和生理调控与phoB（pho操纵子的正调节基因）以及phoA（碱性磷酸酶的结构基因）非常相似，这两个基因都可由磷酸盐限制诱导。当从杂交质粒中去除phoR上游的phoB启动子，或者在phoB结构基因中插入转录终止子时，无论培养基中的磷酸盐浓度如何，PhoR蛋白的合成都变得不可诱导。结果表明，phoB和phoR构成一个单一操纵子，其启动子位于phoB近端。细胞中相同低水平的PhoR蛋白可作为phoB-phoR操纵子在磷酸盐有限时的正调节因子和磷酸盐过量时的负调节因子。这些结果表明，操纵子的最大水平是由磷酸盐限制诱导的PhoR蛋白数量增加以及该蛋白作为正调节因子的功能变化共同导致的。
