Gui L, Sunnarborg A, LaPorte D C
Department of Biochemistry, University of Minnesota, Minneapolis, 55455, USA.
J Bacteriol. 1996 Aug;178(15):4704-9. doi: 10.1128/jb.178.15.4704-4709.1996.
The control of the glyoxylate bypass operon (aceBAK) of Escherichia coli is mediated by two regulatory proteins, IclMR and FadR. IclMR is a repressor protein which has previously been shown to bind to a site which overlaps the aceBAK promoter. FAR is a repressor/activator protein which participates in control of the genes of fatty acid metabolism. A sequence just upstream of the iclR promoter bears a striking resemblance to FadR binding sites found in the fatty acid metabolic genes. The in vitro binding specificity of FadR, determined by oligonucleotide selection, was in good agreement with the sequences of these sites. The ability of FadR to bind to the site associated with iclR was demonstrated by gel shift and DNase I footprint analyses. Disruption of FadR or inactivation of the FadR binding site of iclR decreased the expression of an iclR::lacZ operon fusion, indicating that FadR activates the expression of iclR. It has been reported that disruption of fadR increases the expression of aceBAK. We observed a similar increase when we inactivated the FadR binding site of an iclR+ allele. This result suggests that FadR regulates aceBAK indirectly by altering the expression of IclR.
大肠杆菌乙醛酸支路操纵子（aceBAK）的调控由两种调节蛋白IclMR和FadR介导。IclMR是一种阻遏蛋白，先前已证明它能结合到与aceBAK启动子重叠的位点。FadR是一种阻遏/激活蛋白，参与脂肪酸代谢基因的调控。iclR启动子上游的一段序列与脂肪酸代谢基因中发现的FadR结合位点极为相似。通过寡核苷酸筛选确定的FadR体外结合特异性与这些位点的序列高度一致。凝胶迁移和DNase I足迹分析证明了FadR与iclR相关位点的结合能力。FadR的缺失或iclR的FadR结合位点的失活降低了iclR::lacZ操纵子融合体的表达，表明FadR激活了iclR的表达。据报道，fadR的缺失会增加aceBAK的表达。当我们使iclR+等位基因的FadR结合位点失活时，也观察到了类似的增加。这一结果表明，FadR通过改变IclR的表达间接调控aceBAK。
