Hugouvieux-Cotte-Pattat N, Robert-Baudouy J
J Bacteriol. 1987 Mar;169(3):1223-31. doi: 10.1128/jb.169.3.1223-1231.1987.
In the phytopathogenic enterobacterium Erwinia chrysanthemi, the catabolism of hexuronates is linked to the degradation of pectic polymers. We isolated Mu lac insertions in each gene of the hexuronate pathway and used genetic fusions with lacZ (the beta-galactosidase gene of Escherichia coli) to study the regulation of this pathway. Three independent regulatory genes (exuR, uxuR, and kdgR) were found. Galacturonate and glucuronate were converted into 2-keto-3-deoxygluconate (KDG) by separate three-step pathways encoded by the uxaC, uxaB, and uxaA genes and the uxaC, uxuB, and uxuA genes, respectively. The two aldohexuronates entered the cell by a specific transport system, encoded by exuT. Wild-type strain 3937 was unable to use glucuronate as a carbon source since glucuronate was unable to induce the exuT expression. Mutants able to use glucuronate possessed an inactivated exuR gene. The product of the regulatory gene exuR negatively controlled the expression of exuT, uxaC, uxaB, and uxaA, which was inducible in the presence of galacturonate. The two genes specifically involved in glucuronate catabolism, uxuA and uxuB, formed two independent transcriptional units regulated separately, uxuB expression was not inducible, whereas uxuA expression was induced in the presence of glucuronate and controlled by the uxuR product. KDG, the common end product of both pathways, is cleaved by the kdgK and kdgA gene products. KDG enters the cell by a specific transport system, encoded by kdgT. The regulatory gene kdgR controlled the expression of kdgT, kdgK, and kdgA and partially that of the pel genes encoding pectate-lyases. The real inducer of pectate-lyase synthesis, originating from catabolism of galacturonate or glucuronate, appeared to be KDG. The genes of E. chrysanthemi affecting hexuronate catabolism are separated into six independent transcriptional units exuT, uxaCBA, uxuA, uxuB, kdgK, and kdgA, but only three gene clusters were localized on the genetic map: exuT-uxaCBA, uxuA-uxuB-kdgK, and kdgA-exuR.
在植物病原性肠道细菌菊欧文氏菌中，己糖醛酸的分解代谢与果胶聚合物的降解相关。我们分离了己糖醛酸途径各基因中的Mu lac插入突变体，并利用与lacZ（大肠杆菌的β-半乳糖苷酶基因）的基因融合来研究该途径的调控。发现了三个独立的调控基因（exuR、uxuR和kdgR）。半乳糖醛酸和葡萄糖醛酸分别通过由uxaC、uxaB和uxaA基因以及uxaC、uxuB和uxuA基因编码的独立三步途径转化为2-酮-3-脱氧葡萄糖酸（KDG）。这两种醛糖醛酸通过由exuT编码的特定转运系统进入细胞。野生型菌株3937不能利用葡萄糖醛酸作为碳源，因为葡萄糖醛酸不能诱导exuT表达。能够利用葡萄糖醛酸的突变体具有失活的exuR基因。调控基因exuR的产物负向控制exuT、uxaC、uxaB和uxaA的表达，这些基因在半乳糖醛酸存在时是可诱导的。专门参与葡萄糖醛酸分解代谢的两个基因uxuA和uxuB形成两个独立的转录单元，分别受到调控，uxuB的表达不可诱导，而uxuA的表达在葡萄糖醛酸存在时被诱导，并受uxuR产物的控制。KDG是两条途径的共同终产物，由kdgK和kdgA基因产物裂解。KDG通过由kdgT编码的特定转运系统进入细胞。调控基因kdgR控制kdgT、kdgK和kdgA的表达，并部分控制编码果胶酸裂解酶的pel基因的表达。果胶酸裂解酶合成的真正诱导物似乎源自半乳糖醛酸或葡萄糖醛酸的分解代谢，是KDG。影响己糖醛酸分解代谢的菊欧文氏菌基因被分为六个独立的转录单元exuT、uxaCBA、uxuA、uxuB、kdgK和kdgA，但只有三个基因簇定位在遗传图谱上：exuT-uxaCBA、uxuA-uxuB-kdgK和kdgA-exuR。
