A number of cDNA clones whose products may interact with D1 receptors in vivo were identified. One of the clones, P24, was characterized further. P24 is localized in dendrites and spines of pyramidal cells in PFC. The extent of overlap between P24 expressing and D1 receptor expressing pyramidal cells appeared to be 100%. In contrast, only a limited number D1 receptor antibody labeled neurons in caudate expressed P24. P24 lowers the threshold of D1 receptor response to dopamine (DA) by an order of magnitude. Sequence similarity suggests P24 is a diverged member of the RAMP family. The P24 protein is therefore referred to as a D1 DA RAMP, calcyon. The isolated protein and nucleotide molecule encoding the protein, as well as primers for the nucleotide, are described. The protein and compounds modifying DA binding to the receptor or calcium release which is mediated by the Calcyon, are useful in research studies, drug screening, and therapeutically.