Gel mobility shift assay of the usp1 and usp2 regulatory regions using QsmR-His, His-RpoS, and E. coli RNA core enzyme. (A and B) Binding of QsmR-His to the usp1 (A) and usp2 (B) regulatory regions. (C and D) Binding of RpoS, core enzyme, or RpoS-RNA holoenzyme to the usp1 (C) and usp2 (C) regulatory regions. CI, CII, and CIII indicate DNA-protein complexes I, II, and III, respectively, and F denotes free DNA.