GdhR directly represses <i>lctP</i> transcription. AyalaJulio C. ShaferWilliam M. 2019 <p>A. <i>In vitro</i> transcription was conducted in the presence of increasing concentrations of purified GdhR and 50 nM RNAPσ70 using as template a DNA fragment encoding <i>lctP</i> promoter from -192 to +381 relative to TSS (<i>lctP</i> WT) and the same fragment harboring a 21 bp deletion in the FadR consensus DNA-binding motif (<i>lctP</i>ΔFadR). The size of the <i>lctP</i> transcript peaks is given at the top x axis. Purified MtrR protein was used as specificity control of the transcription inhibition reaction. B. Transcription inhibition curves were generated by plotting the height of the peaks (considering the 0 μM protein reaction as the 100% transcription point) vs. transcription factor molar concentration. (C) Binding of GdhR to WT <i>lctP</i> promoter from -192 to +99 relative to the TSS (<i>lctP</i> WT) and to the same promoter fragment harboring the 21 bp deletion in the FadR DNA-binding motif (<i>lctP</i>ΔFadR) was compared by EMSA. (D) GdhR binding curves to the WT and mutant <i>lctP</i> probes and the dissociation constant (Kd) were determined by densitometry from the EMSA gels adjusting the data to a nonlinear regression analysis using the Hill equation [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1008233#ppat.1008233.ref069" target="_blank">69</a>].</p>