The binding of Class II sRNA MgrR to two different sites on matchmaker protein Hfq enables efficient competition for Hfq and annealing to regulated mRNAs

MgrR efficiently displaces both A₂₇ and U₁₈ from the complex with Hfq. (A) The dissociation of ³²P-A₂₇ or ³²P-U₁₈ from Hfq, which was initiated by unlabeled MgrR sRNA, A₂₇, or U₁₈, was monitored by a double-filter retention assay. The data were fit to the three-parameter equation for unlabeled A₂₇ and U₁₈ and and to the four-parameter equation for unlabeled MgrR sRNA, as described in Materials and Methods. (B) The average IC₅₀ values for the competition against ³²P-A₂₇ or ³²P-U₁₈. The average values of Hill coefficients in the fitting were −3.2 ± 1.2 for MgrR competition against ³²P-A₂₇, and −3.3 ± 1.8 for MgrR competition against ³²P-U₁₈. Bars marked with (*) correspond to IC₅₀ values, which were estimated as higher than 100 nM.