Pedersen H, Dall J, Dandanell G, Valentin-Hansen P
Department of Molecular Biology, Odense University, Denmark.
Mol Microbiol. 1995 Sep;17(5):843-53. doi: 10.1111/j.1365-2958.1995.mmi_17050843.x.
Repression by CytR depends on the formation of nucleoprotein complexes in which the CytR repressor and the cAMP-CRP activator complex bind co-operatively to the DNA. Transcription initiation from CytR-regulated promoters requires cAMP-CRP; therefore, the cAMP-CRP complex functions both as an activator and as a co-repressor in these promoters. Another interesting aspect of the CytR regulon is that each promoter appears to have individual features. Therefore, structural and functional rules governing the formation of repression and activation complexes in one promoter may not be valid for other promoters of the CytR regulon. Here we show that the Escherichia coli nupG gene contains one CytR- and four CRP-binding sites in the control region. Notably, the architecture of the CytR binding site is different from previously described targets. In addition, the CytR repressor triggers a DNA repositioning of a cAMP-CRP complex in the -35 region upon binding to its operator. Thus, formation of the repression and activation complexes at the nupG promoter involves different subsets of CRP-binding sites. These findings show that the bacterium uses positive and negative regulatory modules to differentially control the expression of CytR- and cAMP-CRP-regulated genes.
CytR的抑制作用取决于核蛋白复合物的形成，其中CytR阻遏物和cAMP-CRP激活复合物协同结合到DNA上。从CytR调控的启动子起始转录需要cAMP-CRP；因此，cAMP-CRP复合物在这些启动子中既作为激活剂又作为共阻遏物发挥作用。CytR调控子的另一个有趣方面是每个启动子似乎都有各自的特点。因此，在一个启动子中控制抑制和激活复合物形成的结构和功能规则可能不适用于CytR调控子的其他启动子。在这里，我们表明大肠杆菌nupG基因在控制区域含有一个CytR结合位点和四个CRP结合位点。值得注意的是，CytR结合位点的结构不同于先前描述的靶点。此外，CytR阻遏物在结合其操纵子时会触发-35区域中cAMP-CRP复合物的DNA重定位。因此，nupG启动子处抑制和激活复合物的形成涉及CRP结合位点的不同子集。这些发现表明，细菌利用正调控和负调控模块来差异控制CytR和cAMP-CRP调控基因的表达。
