RcsC is a membrane-bound protein that is able to sense extracellular changes in temperature, overexpression of membrane protein, and osmolarity [11, 18, 27]. RcsC is a hybrid kinase, contains both an H1 and D1 domain, and is able to transfer phosphoryl groups to the conserved Hpt domain of RcsD [11, 11, 14]. RcsC and RcsD are inner membrane proteins that are involved in the phosphorylation of RcsB in response to environmental signals [11, 28]. Once phosphorylated, the RcsB protein is a positive regulator and it increases the affinity for the specific DNA-binding sites and controls the transcriptional expression of operons [5, 11, 15, 17, 18, 19]. Lys180 is a residue that is located within the predicted DNA-binding motif for RcsB transcriptional regulation. N^ε-Lysine modulates through this residue the RcsB-dependent repression of the flhDC operon [29]. The RcsB/RcsA complex has major affinity for binding sites of which RcsB is only one. The homodimers of RcsB activate transcription, interacting with the RNA polymerase, by overlapping the -35 box of the core promoter; the central position of the binding site is located near bp -41.5 [11, 19, 22, 23, 24, 25]. The formation of heterodimers between RcsB and the RcsA auxiliary protein stabilizes interactions with the distant binding sites [3, 5, 7, 8, 11, 21]. The amount of RcsA protein is limited both by its rapid degradation by two proteases, Lon and ClpYQ, and by its low level of synthesis [6, 11, 20, 30, 31, 32, 33, 34, 35]. RcsB, which belongs to the two-component family, shows a helix-turn-helix motif for interaction with DNA in the C-terminal domain, while the the N-terminal domain is typical of the response regulator [11]. The rcsA gene expression was upregulated in a mutant deficient for the |FRAME: EG11495-MONOMER | HdeD [36] Reviews: [11, 14]