RAMP3 belongs to the RAMP family. Members of this family are single-transmembrane-domain proteins, called receptor (calcitonin) activity modifying proteins (RAMPs). RAMPs have a wide biological distribution; high concentrations are found in the brain, lung, liver, heart and spleen with lower expression levels present in the testes, gastrointestinal tract and thyroid. RAMPs are type I transmembrane proteins with an extracellular N terminus and a cytoplasmic C terminus. They are required to transport calcitonin-receptor-like receptor (CRLR) to the plasma membrane. CRLR, a receptor with seven transmembrane domains, can function as either a calcitonin gene-related peptide (CGRP) receptor or an adrenomedullin receptor, depending on which members of the RAMP family are expressed. In the presence of RAMP3 protein, CRLR functions as an adrenomedullin receptor.