Band 7.2b is an integral phosphoprotein absent from the erythrocyte membranes of patients with hydrocytosis, an autosomal, dominantly inherited, hemolytic anemia characterized by stomatocytic red blood cells with abnormal permeability to Na+ and K+. The role of this protein in the erythrocyte membrane is not well understood. To gain additional insight into the structure and function of this protein, we have cloned the murine band 7.2b cDNA and studied its tissue-specific expression. 2,873 bp of cDNA with an open reading frame of 852 bp were isolated. This fragment encodes a protein of 284 amino acids with a predicted molecular weight of 31 kD. The band 7.2b gene had a wide pattern of expression, with high levels of mRNA in heart, liver, skeletal muscle, and testis and low levels in lung, brain, and spleen. Using fluorescent in situ hybridization, the murine band 7.2b gene was mapped to chromosome 2, at the border of the distal region of 2B and proximal region of C1, syntenic to 9q33-q34, the location of the human homologue. Models of the predicted protein structure showed a short NH2-terminal head, a strongly hydrophobic 28-amino acid stretch presumably encoding a single membrane-spanning domain, and a large domain composed of beta sheet and alpha helix. Database searching showed no significant homology of other known proteins to murine or human band 7.2b.