A full-length cDNA encoding a human-origin G protein-coupled receptor protei n is isolated by screening a human hippocampus library. Also, a rat-origin cDN A corresponding to the above human-origin cDNA is isolated. Proteins encoded b y these cDNAs have an activity of lowering intracellular cAMP concentration under stimulation with histamine. These proteins are usable as tools in screening ligands thereof or in screening candidate compounds for drugs capable of regulating signal transduction from the above proteins.
