Monitoring signal-dependent interactions using a three-hybrid format. (A) A three-hybrid ECLIPSE showing that interaction between calmodulin and CaMKIIα is dependent upon cytosolic Ca2+ levels. Images were captured before and after induction with ionomycin, rapamycin, or both agents. (B) Quantitative analysis showing that both rapamycin and ionomycin are required for endosomal localization of CaMKIIα (n = 1). RFU were normalized against cell fluorescence before induction. (Scale bars,10 μm). Abbreviations: R, mCherry; IM, ionomycin.