Involvement of sigma(54) in exponential silencing of the Pseudomonas putida TOL plasmid Pu promoter
Involvement of sigma(54) in exponential silencing of the Pseudomonas putida TOL plasmid Pu promoter
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DOI：
10.1046/j.1365-2958.1996.345873.x
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发表时间：
1996-01-01
影响因子：
3.6
通讯作者：
PerezMartin, J
中科院分区：
文献类型：
--
作者：
Cases, I;deLorenzo, V;PerezMartin, J
当细胞在培养基中遇到间二甲苯时，恶臭假单胞菌的TOL质粒pWWO的σ（54）依赖性Pu启动子被原核增强子结合XylR蛋白激活。然而，即使在芳香族诱导剂的存在下，在富培养基中细胞的快速指数生长期间，Pu活性在体内被沉默。已知参与控制启动子转录活性的各种元件进行了检查，以确定在指数生长期Pu表达受限的机制。当暴露于间二甲苯时，发现缺失其信号接收N-末端结构域的截短的和完全组成的XylR衍生物经受与野生型XylR相同的指数沉默。这表明该现象不是由于芳香族效应物对XylR的后期激活。整合宿主因子（IHF）结合位点在功能上被静态弯曲DNA片段取代的Pu变体显示出相同的诱导模式，从而排除了生长过程中IHF变化的细胞内水平变化作为导致Pu失活的元素的可能性在快速生长的细胞中。相反，sigma（54）因子的过量产生允许Pu在指数期表达。由于sigma（54）蛋白水平在生长过程中保持大致恒定，Pu的指数沉默可能最终由因子本身活性的变化引起。这种效应可能不是Pu独有的，但可能是sigma（54）依赖性启动子中的一般共调节机制，其将特定基因组的转录与细胞的一般生理状态联系起来。
The sigma(54)-dependent Pu promoter of the TOL plasmid pWWO of Pseudomonas putida becomes activated by the prokaryotic enhancer-binding XylR 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 XylR derivative deleted of its signal-reception N-terminal domain was found to be subjected to the same exponential silencing as the wildtype XylR when exposed to m-xylene. This indicated that the phenomenon is not due to a late activation of XylR 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 sigma(54) factor allowed Pu expression during exponential phase. As sigma(54) 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 sigma(54)-dependent promoters that connects transcription of a specific set of genes with the general physiological status of the cells.