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.