Inouye S, Nakazawa A, Nakazawa T
Proc Natl Acad Sci U S A. 1987 Aug;84(15):5182-6. doi: 10.1073/pnas.84.15.5182.
The regulatory gene xylS on the TOL plasmid of Pseudomonas putida activates the transcription of the xylDLEGF operon for the m-toluate-degrading pathway in the presence of m-toluate. The gene also activates the transcription of the same operon in the presence of m-xylene or m-methylbenzyl alcohol, but for this activation another regulatory gene, xylR, is required. In this study we examined the xylS expression by determining the mRNA by reverse transcriptase mapping and by monitoring the enzyme activity of the xylE gene product, which was expressed under the control of the xylS promoter. The results of the above experiments provide evidence that xylR positively controls the transcription of xylS in the presence of m-xylene or m-methylbenzyl alcohol. The xylS product thus amplified may in turn activate the xylDLEGF operon. The nucleotide sequence of the xylS promoter resembles that of the promoter of the xylCAB operon for the m-xylene-degrading pathway, which is also activated by xylR in the presence of m-xylene or m-methylbenzyl alcohol. In addition, we have demonstrated that the expression of xylR is negatively controlled by its own product. On the basis of these findings, we propose a revised model for the regulation of expression of xyl genes on the TOL plasmid.
恶臭假单胞菌TOL质粒上的调控基因xylS在间甲苯酸存在时可激活间甲苯酸降解途径的xylDLEGF操纵子的转录。该基因在间二甲苯或间甲基苄醇存在时也可激活同一操纵子的转录，但这种激活需要另一个调控基因xylR。在本研究中，我们通过逆转录酶图谱法测定mRNA以及监测在xylS启动子控制下表达的xylE基因产物的酶活性，来检测xylS的表达。上述实验结果提供了证据，表明在间二甲苯或间甲基苄醇存在时，xylR正向控制xylS的转录。如此扩增的xylS产物可能反过来激活xylDLEGF操纵子。xylS启动子的核苷酸序列类似于间二甲苯降解途径的xylCAB操纵子的启动子，后者在间二甲苯或间甲基苄醇存在时也由xylR激活。此外，我们还证明了xylR的表达受其自身产物的负调控。基于这些发现，我们提出了一个关于TOL质粒上xyl基因表达调控的修订模型。
