The AraC/XylS family activator RhaS negatively autoregulates rhaSR expression by preventing cyclic AMP receptor protein activation.
The AraC/XylS family activator RhaS negatively autoregulates rhaSR expression by preventing cyclic AMP receptor protein activation.
复制标题
AraC/XylS 家族激活剂 RhaS 通过阻止环 AMP 受体蛋白激活来负向自动调节 rhaSR 表达。
DOI：
10.1128/jb.00829-08
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发表时间：
2010
影响因子：
3.2
通讯作者：
Egan,SusanM
中科院分区：
文献类型：
--
作者：
Wickstrum,JasonR;Skredenske,JeffM;Balasubramaniam,Vinitha;Jones,Kyle;Egan,SusanM
大肠杆菌RhaR蛋白在其效应物L鼠李糖存在的情况下激活HSR操纵子的表达。由此产生的rHAS蛋白(plusl-鼠李糖)分别激活l-鼠李糖分解代谢操纵子和运输操纵子rhaBADand rhaT的表达。在这里，我们进一步研究了我们先前的发现，rhaS缺失导致rhaSR启动子活性增加三倍，表明rHASR具有负的自身调节。我们发现，RHAS的自动调节需要环状AMP受体蛋白(CRP)结合位点atrhaSR，并且rHas能够与Rhar结合位点atrhaSR结合。与预期的抑制相反，我们发现在缺乏Rhar和rHAR启动子上的CRP结合位点的情况下，rHas激活了表达，达到了与同一启动子的Rhar激活相当的水平。然而，当启动子包含RHAR和CRP结合位点时，RHAS和CRP的激活水平远低于RHAR和CRP，提示CRP不能与RHAS完全共激活。综上所述，我们的结果表明，RHAS的负自动调节涉及RHAS与RHAR竞争结合RHAR结合部位。尽管RHAS和RHAR激活SR转录的水平相似，但CRP不能有效地与RHAS共激活。因此，一旦rhaS达到相对较高的蛋白质浓度，推测足以饱和rhaS激活的启动子，rhaSR转录就会减少。我们提出了一个模型，在该模型中，RHAS和RHAR对DNA的不同弯曲可能是CRP共激活差异的基础。
TheEscherichia coliRhaR protein activates expression of therhaSRoperon in the presence of its effector,l-rhamnose. The resulting RhaS protein (plusl-rhamnose) activates expression of thel-rhamnose catabolic and transport operons,rhaBADandrhaT, respectively. Here, we further investigated our previous finding thatrhaSdeletion resulted in a threefold increase inrhaSRpromoter activity, suggesting RhaS negative autoregulation ofrhaSR. We found that RhaS autoregulation required the cyclic AMP receptor protein (CRP) binding site atrhaSRand that RhaS was able to bind to the RhaR binding site atrhaSR. In contrast to the expected repression, we found that in the absence of both RhaR and the CRP binding site at therhaSRpromoter, RhaS activated expression to a level comparable with RhaR activation of the same promoter. However, when the promoter included the RhaR and CRP binding sites, the level of activation by RhaS and CRP was much lower than that by RhaR and CRP, suggesting that CRP could not fully coactivate with RhaS. Taken together, our results indicate that RhaS negative autoregulation involves RhaS competition with RhaR for binding to the RhaR binding site atrhaSR. Although RhaS and RhaR activaterhaSRtranscription to similar levels, CRP cannot effectively coactivate with RhaS. Therefore, once RhaS reaches a relatively high protein concentration, presumably sufficient to saturate the RhaS-activated promoters, there will be a decrease inrhaSRtranscription. We propose a model in which differential DNA bending by RhaS and RhaR may be the basis for the difference in CRP coactivation.