Zielinski N A, Maharaj R, Roychoudhury S, Danganan C E, Hendrickson W, Chakrabarty A M
Department of Microbiology and Immunology, University of Illinois College of Medicine, Chicago 60612.
J Bacteriol. 1992 Dec;174(23):7680-8. doi: 10.1128/jb.174.23.7680-7688.1992.
The exopolysaccharide alginate is a major virulence factor of Pseudomonas aeruginosa strains that infect the lungs of cystic fibrosis patients. The synthesis of alginate is almost uniquely associated with the pathogenicity of P. aeruginosa within the environment of the cystic fibrosis lung. The gene algC is one of the essential alginate biosynthetic genes and codes for the enzyme phosphomannomutase. In this report, we present data on the transcriptional regulation of algC expression. The activity of the algC promoter is modulated by the response regulator, AlgR1, a member of the two-component signal transduction protein family, which also regulates other alginate-specific promoters. In both mucoid (alginate-positive) and nonmucoid (alginate-negative) P. aeruginosa strains, transcriptional activation of algC increased with the osmolarity of the culture medium. This osmolarity-induced activation was found to be dependent on AlgR1. AlgR1 was found to interact directly with the algC promoter. Deletion mapping, in conjunction with mobility shift assays, showed that AlgR1 specifically bound with two regions of algC upstream DNA. A fragment spanning nucleotide positions -378 to -73 showed strong specific binding, while a fragment located between positions -73 and +187 interacted relatively weakly with AlgR1. Phosphorylation of the AlgR1 protein resulted in the stimulation of its in vitro ability to bind to the algC promoter region (a fragment spanning nucleotides -378 to -73). Transcription from the algC promoter, which has significant homology with the RNA polymerase sigma-54 (RpoN) recognition sequence, decreased in an rpoN mutant of P. aeruginosa.
胞外多糖藻酸盐是感染囊性纤维化患者肺部的铜绿假单胞菌菌株的主要毒力因子。藻酸盐的合成几乎唯一地与铜绿假单胞菌在囊性纤维化肺部环境中的致病性相关。algC基因是藻酸盐生物合成的必需基因之一，编码磷酸甘露糖变位酶。在本报告中，我们展示了关于algC表达转录调控的数据。algC启动子的活性受响应调节因子AlgR1调控，AlgR1是双组分信号转导蛋白家族的成员，它也调控其他藻酸盐特异性启动子。在黏液型（藻酸盐阳性）和非黏液型（藻酸盐阴性）铜绿假单胞菌菌株中，algC的转录激活随培养基渗透压的升高而增加。发现这种渗透压诱导的激活依赖于AlgR1。发现AlgR1直接与algC启动子相互作用。缺失作图结合迁移率变动分析表明，AlgR1与algC上游DNA的两个区域特异性结合。一个跨越核苷酸位置-378至-73的片段显示出强特异性结合，而位于位置-73和+187之间的片段与AlgR1的相互作用相对较弱。AlgR1蛋白的磷酸化导致其体外结合algC启动子区域（一个跨越核苷酸-378至-73的片段）的能力增强。与RNA聚合酶sigma-54（RpoN）识别序列具有显著同源性的algC启动子的转录在铜绿假单胞菌的rpoN突变体中减少。
