The green fluorescent protein (GFP) of the jellyfish Aequorea victoria is an emerging tool to monitor gene expression in situ and in vivo. Because of its fluorescence properties, when GFP is fused in-frame to a specific protein of interest, various aspects of the behavior of this protein can be analyzed noninvasively. Here we describe a fusion between GFP and human calmodulin-like protein (CLP) and show that this protein retains fluorescence and known characteristics of CLP, including Ca(2+)-dependent interaction with phenyl-Sepharose and interaction with a specific cellular target protein. The results suggest a novel application for GFP fusion proteins in the rapid, nonradioactive detection of interacting proteins on gel overlays.