ITC-based interaction between sRNA, AbsR25 and Hfq truncations. 1 μm protein samples were titrated with 25 μm AbsR25 over a series of injections, and binding affinities (dissociation constant, Kd) were determined for Hfq66 (A), Hfq72 (B), Hfq92 (C), and Hfq168 (D).