Braun Volkmar, Mahren Susanne, Sauter Annette
Microbiology/Membrane Physiology, University of Tübingen, Auf der Morgenstelle 28, Tübingen 72096, Germany.
Biometals. 2005 Oct;18(5):507-17. doi: 10.1007/s10534-005-3497-0.
Studies of the ferric citrate transport genes in Escherichia coli K-12 have revealed a novel type of transcriptional regulation. The inducer, ferric citrate, binds to an outer membrane protein and must not be transported into the cells to initiate transcription of the ferric citrate transport genes. Rather, a signaling cascade from the cell surface across the outer membrane, the periplasm, and the cytoplasmic membrane into the cytoplasm transmits information on the presence of the inducer in the culture medium into the cytoplasm, where gene transcription occurs. The outer membrane protein FecA serves as a signal receiver and as a signal transmitter across the outer membrane. The FecR protein serves as a signal receiver in the periplasm and as a signal transmitter across the cytoplasmic membrane into the cytoplasm, where the FecI sigma factor is activated to bind RNA polymerase and specifically initiate transcription of the fecABCDE transport genes by binding to the promoter upstream of the fecA gene. Transcription of the fecI fecR regulatory genes is repressed by Fe(2+) bound to the Fur repressor protein. Under iron-limiting conditions, Fur is not loaded with Fe(2+), the fecI and fecR genes are transcribed, and the FecI and FecR proteins are synthesized and respond to the presence of ferric citrate in the medium when ferric citrate binds to the FecA protein. Regulation of the fec genes represents the paradigm of a growing number of gene regulation systems involving transmembrane signaling across three cellular compartments.
对大肠杆菌K-12中铁柠檬酸转运基因的研究揭示了一种新型的转录调控方式。诱导物铁柠檬酸与一种外膜蛋白结合，且在启动铁柠檬酸转运基因转录之前不能被转运到细胞内。相反，从细胞表面穿过外膜、周质和细胞质膜进入细胞质的信号级联反应，将培养基中诱导物存在的信息传递到发生基因转录的细胞质中。外膜蛋白FecA作为信号接收器，并作为跨外膜的信号传递器。FecR蛋白作为周质中的信号接收器，并作为跨细胞质膜进入细胞质的信号传递器，在细胞质中，FecI σ因子被激活以结合RNA聚合酶，并通过结合fecA基因上游的启动子来特异性启动fecABCDE转运基因的转录。fecI fecR调控基因的转录被与Fur阻遏蛋白结合的Fe(2+)所抑制。在铁限制条件下，Fur未结合Fe(2+)，fecI和fecR基因被转录，FecI和FecR蛋白被合成，当铁柠檬酸与FecA蛋白结合时，它们会对培养基中铁柠檬酸的存在做出反应。fec基因的调控代表了越来越多涉及跨三个细胞区室进行跨膜信号传导的基因调控系统的范例。
