Involvement of σ54 in exponential silencing of the Pseudomonas putida TOL plasmid Pu promoter
Involvement of σ54 in exponential silencing of the Pseudomonas putida TOL plasmid Pu promoter
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σ54 参与恶臭假单胞菌 TOL 质粒 Pu 启动子的指数沉默
DOI：
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
J. Pérez
中科院分区：
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作者：
IIdefonso Cases;V. Lorenzo;J. Pérez
恶臭假单胞菌TOL质粒σ54依赖的Pu启动子被原核增强子结合的XyIR蛋白激活。然而，即使在芳香诱导剂的存在下，Pu的活性在体内也是沉默的，因为细胞在富含介质中快速指数生长。研究了控制启动子转录活性的各种已知元件，以确定Pu在指数生长阶段的表达受到限制的机制。信号接收N-末端结构域被删除的截短和完全构成的XyIR衍生物在暴露于间二甲苯时，受到与野生型XyIR相同的指数沉默。这表明这一现象不是由于芳香族效应器对XyIR的晚期激活所致。其中整合宿主因子(IHF)结合位点在功能上被静态弯曲的DNA片段取代的Pu变体显示了相同的诱导模式，从而排除了IHF在生长过程中细胞内水平变化的可能性，这是导致快速生长细胞中Pu不活性的原因。相反，σ54因子的过量生产允许Pu在指数期表达。由于σ54蛋白水平在生长过程中基本保持不变，Pu的指数沉默最终可能是由该因子本身的活性变化引起的。这种效应可能不是Pu独有的，而可能是σ54依赖的启动子中的一种普遍的共同调节机制，它将一组特定基因的转录与细胞的一般生理状态联系起来。
The σ54‐dependent Pu promoter of the TOL plasmid pWWO of Pseudomonas putida becomes activated by the prokaryotic enhancer‐binding XyIR protein when cells encounter m‐xylene in the medium. However, even in the presence of the aromatic inducer, Pu activity is silenced in vivo during rapid exponential growth of the cells in rich medium. Various elements known to be involved in the control of the transcriptional activity of the promoter were examined to ascertain the mechanism by which expression of Pu is limited during the exponential phase of growth. A truncated and fully constitutive XyIR derivative deleted of its signal reception N‐terminal domain was found to be subjected to the same exponential silencing as the wild‐type XyIR when exposed to m‐xylene. This indicated that the phenomenon is not due to a late activation of XyIR by the aromatic effector. A Pu variant in which the integration host factor (IHF)‐binding site had been functionally replaced by a statically curved DNA segment showed the same induction pattern, thus ruling out variations in the intracellular levels of IHF changes during growth as the element responsible for the inactivity of Pu in rapidly growing cells. On the contrary, overproduction of the σ54 factor allowed Pu expression during exponential phase. As σ54 protein levels remained approximately constant during growth, the exponential silencing of Pu could be caused ultimately by changes in the activity of the factor itself. This effect may not be exclusive to Pu, but could be a general co‐regulation mechanism in σ54‐dependent promoters that connects transcription of a specific set of genes with the general physiological status of the cells.