provided evidence that the transcription of the gadXW operon is regulated to a posttranscriptional level by a gadY small RNA [4, 11] GadW is highly homologous to GadX (42%), and apparently both are capable of cross talk to regulate expression of the genes of this system [4] Although little is known about the regulating mechanism of GadW, Tucker et al. proposed that this regulator and GadX have distinct molecular mechanisms [2, 3] These regulators form homodimers [8] and heterodimers [1]in vivo. Currently, the GadW/GadX-dependent circuit, involved in the GAD system, is under discussion and study. Tramonti et al. showed that GadX alone activates gadA and gadB promoters [10] Ma et al. added to this regulatory interaction with the GadW protein, showing that it inhibits GadX and that in some cases it activates in the absence of GadX [1] Trucker et al. gave evidence that GadW can work as a coactivator of GadX or it can inhibit the GadX-dependent activation; they also provided evidence of more target genes for GadX/GadW regulation [3] Regarding these interactions, Tramonti et al. showed the direct GadX binding at promoters of the gadB (two sites) and gadA (four sites) operons [10] also, Ma et al. showed that GadW forms a homodimer and that it also binds to the DNA of the gadA and gadB promoters [1] As a member of the AraC/XylS family, this transcription factor is composed of two domains: the C-terminal domain (60% homologous to the C terminal of GadX), which contains two potential helix-turn-helix DNA-binding motifs in the DNA-binding region, and the amino-terminal domain (30% homologous to the N terminal of GadX), which is responsible for dimerization [1, 8, 12] Tramonti et al. speculated that GadW binds in tandem to two directed repeat sequences, in the same orientation, in the intergenic regions to activate or repress the transcription of the genes regulated [4] The binding targets for GadW consist of 21-nucleotide-long directed repeat sequences that possess conserved motifs, called the GAD box, which is proposed to be the binding site for GadW and GadX [3, 3, 4] This proposal was not unexpected, because the identity and similarity of the C-terminal domains are 41% and 66%, respectively [4] Each monomer of GadW binds to one of these conserved sequences [4]