Fig. 4.

RelA stimulates RNA binding by Hfq. (A) RelA stimulates complex formation of RyhB with otherwise ineffective amounts of Hfq. Gel mobility shift of labeled RyhB incubated with Hfq and/or RelA purified from wild-type or hfq⁻ cells. Bound and unbound labeled RyhB is indicated. (B) RyhB binding by Hfq in the presence of BSA or RelA (purified from hfq⁻). (C) The apparent dissociation constant of Hfq-RyhB is ∼120 nM. The value of K_app decreases dramatically in the presence of RelA, and RyhB binds Hfq with a much higher affinity (2.5 nM).