Johnson D I, Somerville R L
Mol Gen Genet. 1984;195(1-2):70-6. doi: 10.1007/BF00332726.
The gene ileR+, considered to encode a transacting protein involved in the regulation of the thr and ilv operons of Escherichia coli, has been cloned and localized to a 1.2 Kb BglII-SalI fragment of DNA. In strains harboring attenuation-defective fusions of lacZ to the promoter regions of the thr and ilv operons, ileR mutations lead to beta-galactosidase levels higher than those of the deattenuated parental strains. Reduced utilization of the thr and ilv promoters was observed in ileR cells harboring either ilvR+ plasmids or plasmids leading to the hyperproduction of Trp repressor. These results support the idea that ileR+ encodes a repressor protein that negatively affects the expression of the thr and ilv operons. Two additional trans-acting positive regulatory elements that act at the thr and ilv promoters have been identified by an analysis of deletion mutants. It thus appears that there exist positive as well as negative controlling elements that can act independently of attenuation to modulate the ilv and thr operons.
基因ileR +被认为编码一种参与大肠杆菌苏氨酸（thr）和异亮氨酸-缬氨酸（ilv）操纵子调控的反式作用蛋白，该基因已被克隆并定位到一段1.2千碱基对（Kb）的BglII - SalI DNA片段上。在含有lacZ与thr和ilv操纵子启动子区域的衰减缺陷型融合体的菌株中，ileR突变导致β-半乳糖苷酶水平高于去衰减亲代菌株。在携带ilvR +质粒或导致色氨酸阻遏物超量产生的质粒的ileR细胞中，观察到thr和ilv启动子的利用减少。这些结果支持ileR +编码一种阻遏蛋白的观点，该阻遏蛋白对thr和ilv操纵子的表达产生负向影响。通过对缺失突变体的分析，已鉴定出另外两个作用于thr和ilv启动子的反式作用正调控元件。因此，似乎存在可以独立于衰减作用来调节ilv和thr操纵子的正向和负向控制元件。
