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. 2017 Aug 3;8:1466. doi: 10.3389/fmicb.2017.01466

FIGURE 5.

FIGURE 5

The sigma 19 (FecI) GENSOR unit. In the presence of ferric dicitrate, FecI activates transcription of genes that code for proteins involved in transport of ferric dicitrate. Events occur as follows: external ferric dicitrate binds to FecA and causes a conformational change that allows FecA binding to TonB. FecA, TonB, and ExbD, and ExbB forms a complex that transports external ferric dicitrate into the periplasmic space. Alternatively, this complex binds to FecR, a protein that binds to sigma 19 and stimulates the binding of sigma 19 to RNA polymerase. Finally, the complex stimulates the transcription of the genes that code for proteins involved in the transport of ferric dicitrate from the periplasmic space to the cytoplasm. The signal and signal transduction is shown in blue, the genetic switch is shown in yellow, and the response is shown in green.