Zhang Aixia, Rosner Judah L, Martin Robert G
Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-0560, USA.
Mol Microbiol. 2008 Sep;69(6):1450-5. doi: 10.1111/j.1365-2958.2008.06371.x. Epub 2008 Jul 31.
The Escherichia coli tolC encodes a major outer membrane protein with multiple functions in export (e.g. diverse xenobiotics, haemolysin) and as an attachment site for phage and colicins. tolC is regulated in part by MarA, SoxS and Rob, three paralogous transcriptional activators which bind a sequence called the marbox and which activate multiple antibiotic and superoxide resistance functions. Two previously identified tolC promoters, p1 and p2, are not regulated by MarA, SoxS or Rob but p2 is activated by EvgAS and PhoPQ which also regulate other functions. Using transcriptional fusions and primer extension assays, we show here that tolC has two additional strong overlapping promoters, p3 and p4, which are downstream of p1, p2 and the marbox and are activated by MarA, SoxS and Rob. p3 and p4 are configured so that a single marbox suffices to activate transcription from both promoters. At the p3 promoter, the marbox is separated by 20 bp from the -10 hexamer for RNA polymerase but at the p4 promoter, the same marbox is separated by 30 bp from the -10 hexamer. The multiple tolC promoters may allow the cell to respond to diverse environments by co-ordinating tolC transcription with other appropriate functions.
大肠杆菌tolC编码一种主要的外膜蛋白，它在输出过程中具有多种功能（如多种异源生物、溶血素），并且是噬菌体和大肠杆菌素的附着位点。tolC部分受MarA、SoxS和Rob这三种同源转录激活因子调控，它们结合一个称为marbox的序列，并激活多种抗生素和超氧化物抗性功能。两个先前鉴定的tolC启动子p1和p2不受MarA、SoxS或Rob调控，但p2受EvgAS和PhoPQ激活，它们也调控其他功能。通过转录融合和引物延伸分析，我们在此表明tolC还有另外两个强重叠启动子p3和p4，它们位于p1、p2和marbox的下游，并且受MarA、SoxS和Rob激活。p3和p4的配置使得单个marbox足以激活两个启动子的转录。在p3启动子处，marbox与RNA聚合酶的-10六聚体相隔20 bp，但在p4启动子处，相同的marbox与-10六聚体相隔30 bp。多个tolC启动子可能允许细胞通过将tolC转录与其他适当功能协调起来以应对不同环境。
