Analysis of three clustered polygalacturonase genes in Erwinia chrysanthemi 3937 revealed an anti-repressor function for the PecS regulator
Analysis of three clustered polygalacturonase genes in Erwinia chrysanthemi 3937 revealed an anti-repressor function for the PecS regulator
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DOI：
10.1046/j.1365-2958.1999.01609.x
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发表时间：
1999-01-01
影响因子：
3.6
通讯作者：
Hugouvieux-Cotte-Pattat, N
中科院分区：
文献类型：
--
作者：
Nasser, W;Shevchik, VE;Hugouvieux-Cotte-Pattat, N
菊花Erwinia 3937分泌一系列果胶分解酶，包括几种由pel基因编码的果胶分解酶。我们发现了一个由pehV、pehW和pehX三个相邻基因组成的新的果胶分解基因簇，其产物具有聚半乳糖醛酸酶活性。这三个基因之间的高度相似性表明它们是祖先基因复制的结果。pehV、pehW和pehX的转录依赖于几种环境条件。它们是由果胶分解代谢产物诱导的，这种诱导是由于控制果胶分解代谢几乎所有步骤的KdgR抑制因子失活。钙离子的存在强烈地降低了三个peh基因的转录。它们的表达也受生长阶段、渗透压、限氧和氮饥饿的影响。此外，pehX的转录受分解代谢抑制的影响，并受激活蛋白CRP的控制。PecS最初被分离为毒力因子的抑制因子，可作为peh转录的激活因子。我们发现三种调节因子KdgR， PecS和CRP通过与peh基因的启动子区域直接相互作用而起作用。对KdgR、PecS、CRP和RNA聚合酶同时结合的分析表明，PecS的激活作用是PecS和KdgR竞争占据重叠结合位点的结果。因此，为了激活peh转录，PecS作为KdgR的抗抑制因子。
Erwinia chrysanthemi 3937 secretes an arsenal of pectinolytic enzymes including several pectate lyases encoded by the pel genes. We characterized a novel cluster of pectinolytic genes consisting of the three adjacent genes pehV, pehW and pehX, whose products have polygalacturonase activity. The high similarity between the three genes suggests that they result from duplication of an ancestral gene. The transcription of pehV, pehW and pehX is dependent on several environmental conditions. They are induced by pectin catabolic products and this induction results from inactivation of the KdgR repressor which controls almost all the steps of pectin catabolism. The presence of calcium ions strongly reduced the transcription of the three peh genes. Their expression was also affected by growth phase, osmolarity, oxygen limitation and nitrogen starvation. In addition, the pehX transcription is affected by catabolite repression and controlled by the activator protein CRP. PecS, which was initially isolated as a repressor of virulence factors, acts as an activator of the peh transcription. We showed that the three regulators KdgR, PecS and CRP act by direct interaction with the promoter regions of the peh genes. Analysis of simultaneous binding of KdgR, PecS, CRP and RNA polymerase indicated that the activator effect of PecS results from a competition between PecS and KdgR for the occupation of overlapping binding sites. Thus, to activate peh transcription, PecS behaves as an anti-repressor against KdgR.