Like CanRch1, Ei24 can bind directly to IMPβ1 and IMPαΔIBB with high affinity. (A) 30 nM of biotinylated (B)-GST-Ei24(N) or B-GST-CanRch1 was added to increasing concentrations of IMPβ1 (top), IMPα2 (bottom), or their mutant derivatives, as indicated, and an AlphaScreen assay was performed (see Materials and methods). Results are for a single experiment (representative of three separate assays), with values calculated as the percentage of binding to IMPβ1 WT or IMPα2ΔIBB, with apparent dissociation constants (K_d) indicated. (B) Pooled data represent the mean percentage of maximal binding (±SEM, error bars; n ≥ 3) to Ei24N/CanRch1 for each IMP relative to that of IMPβ1 WT; p-values are shown for significant differences. IBBm, IBB-binding mutant.