Brünker P, Rother D, Sedlmeier R, Klein J, Mattes R, Altenbuchner J
Institut für Industrielle Genetik, Universität Stuttgart, Germany.
Mol Gen Genet. 1996 Jun 12;251(3):307-15. doi: 10.1007/BF02172521.
The broad-spectrum mercury resistance of Streptomyces lividans 1326 is mediated by six open reading frames (orf). These are arranged in two divergently transcribed operons. The orfs mer A (mercuric reductase) and mer B (organolyase) form one of the two operons. These genes and their regulation were further studied by deletion analysis and transcriptional fusion to the reporter gene xylE in the plasmid pXE4. An increase in XylE activity in response to the presence of mercuric ions was observed. The function of ORF2 (MerT) and ORF3 (MerP) as mercury-specific transport proteins, previously postulated based on the structural features of the predicted proteins, was confirmed. Transcription of the mer genes starts within the intercistronic region and two divergent promoters were identified by S1 nuclease mapping. Expression of the genes was negatively regulated by the product of orf1, now called merR. The repressor function was confirmed by gel retardation assays. MerR, produced in Escherichia coli, bound to two sites (operators) in the fragment containing the promoter region between merA and merR. Addition of mercuric ions and phenylmercuric acetate prevented the binding of MerR.
变铅青链霉菌1326的广谱汞抗性由六个开放阅读框（orf）介导。它们排列在两个反向转录的操纵子中。orf merA（汞还原酶）和merB（有机汞裂解酶）构成两个操纵子之一。通过缺失分析以及与质粒pXE4中的报告基因xylE进行转录融合，对这些基因及其调控进行了进一步研究。观察到响应汞离子的存在，XylE活性增加。先前基于预测蛋白质的结构特征推测的ORF2（MerT）和ORF3（MerP）作为汞特异性转运蛋白的功能得到了证实。mer基因的转录起始于基因间区域内，通过S1核酸酶作图鉴定出两个反向启动子。这些基因的表达受到orf1（现称为merR）产物的负调控。通过凝胶阻滞试验证实了阻遏物功能。在大肠杆菌中产生的MerR与包含merA和merR之间启动子区域的片段中的两个位点（操纵基因）结合。添加汞离子和苯基汞乙酸盐可阻止MerR的结合。
