Acdp1 contains 4 transmembrane domains, 2 CBS domains, a DUF21 domain, and a cNMP-binding domain. Northern blot analysis of mouse tissues detected high Acdp1 expression in brain and lower expression in testis and kidney. Immunohistochemical analysis and confocal imaging revealed Acdp1 in the plasma membrane of cultured mouse hippocampal neurons. In addition, all 4 contain a 31-amino acid sequence motif that is present in the cyclin box, a cyclic nucleotide-monophosphate (cNMP)-binding domain, and 2 CBS domains. The ACDP1 gene, designated CNNM1 by the HUGO Nomenclature Committee, encodes a deduced 951-amino acid protein. Northern blot analysis revealed expression of CNNM1 at high levels in brain and at low levels in testis; no expression was found in any other tissues tested.