The ACDP3 gene, designated CNNM3 by the HUGO Nomenclature Committee, encodes a deduced 707-amino acid protein. Northern blot analysis revealed ubiquitous expression of CNNM3. Immunofluorescence studies showed that all 4 CNMM proteins are predominantly localized in the nucleus. Acdp3 contains 4 transmembrane domains, 2 CBS domains, a DUF21 domain, and a cNMP-binding domain. It also has large alanine- and leucine-rich regions. Northern blot analysis detected variable Acdp3 expression in all mouse tissues examined, with highest expression in brain, kidney, liver, and heart.