The gene for human erythrocyte membrane protein band 7. 2 (EPB72) maps to 9q33-q34 centromeric to the Philadelphia chromosome translocation breakpoint region

Erthrocyte band 7.2b is a 31-kDa integral phosphoprotein absent from the erythrocytes of many patients with hereditary stomatocytosis (HSt). HSt is a heterogeneous group of disorders characterized by mouth-shaped erythrocyte morphology on peripheral blood smears. The clinical severity of HSt is variable; some patients experience hemolysis and anemia while others are asymptomatic. The red cell membranes of these patients usually exhibit abnormal permeability to sodium and potassium with resultant modification of intracellular water content. The band 7.2b protein has been purified and the cDNA cloned. The approved gene name and symbol are erythrocyte membrane protein band 7.2 and EPB72, respectively, as assigned by the Human Gene Nomenclature Committee. Using a human reticulocyte cDNA library as template, a 491-bp fragment corresponding to the 3' end of the coding region of the EPB72 cDNA was amplified. Three overlapping phase DNA clones were isolated using this probe. Four genomic DNA fragments of 2.0, 2.5, 4.5, and 5.0 kb, respectively, were isolated from these clones. To localize the EPB72 gene by fluorescence in situ hybridization, these genomic DNA fragments were labeled with biotin-11-dUTP and hybridized to metaphase chromosomes as described. Probes were preannealed to C[sub 0]t1-fractionated DNA to block repetitive sequences. Experiments were analyzed and digitally imaged using a cooled CCD camera. The probes, in combination, gave specific hybridization signals only in chromosome 9q. The gene for erythrocyte membrane protein 7.2 localized to 9q33-q34.