Figure 4.
The QseC signaling cascade of enterohemorrhagic Escherichia coli. The QseC sensor is activated by autoinducer‐3 (AI‐3) and/or catecholamine hormones [epinephrine (Ep), norepinephrine (Ne)] and phosphorylates its cognate response regulator QseB and two non‐cognate response regulators, QseF and KdpE. Each of the response regulators induces the expression of specific sets of genes shown in boxes. The non‐cognate regulators QseF and KdpE can also be activated by their cognate sensors, QseE and KdpD, respectively. Like QseC, QseE is activated by Ep,Ne but it does not interact with AI‐3, and KdpD senses osmolarity and potassium. In addition, two quorum sensing‐regulated LysR‐type transcriptional regulatory proteins, QseA and sQseD, contribute to the regulation of the LEE locus and QseA also induces the expression of QseEF. FusKR senses fucose and functions to downregulate LEE expression and the expression of the fusKR operon itself can be downregulated by the QseF response regulator.