We have cloned and characterized the Na,K-ATPase β3 subunit gene (ATP1B3), and a β3 subunit pseudogene (ATP1B3P1), from a human PAC genomic library. The β3 subunit gene is >50 kb in size and is split into 7 exons. The exon/intron organization of the β3 subunit gene is identical to that of the Na,K-ATPase β3 subunit gene, indicating that these two genes evolved from a common evolutionary ancestor. Comparison of the promoter region of the human and mouse β3 subunit gene reveals a high degree of homology within a 300-bp segment located immediately upstream of the translation start site, suggesting that control elements that serve to regulate the cell-specific expression of the β3 subunit gene are likely to be located within this conserved region. Dot blot analysis of β3 subunit transcripts revealed expression within virtually all human tissues, while in situ hybridization showed expression of β3 mRNA in both neurons and glia of rat brain. Fluorescence in situ hybridization with PAC DNA clones localized ATP1B3 to the q22 → 23 region of Chromosome (Chr) 3, and the β3 pseudogene to the p13 → 15 region of Chr 2.
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