Abstract
Anion exchange is a nearly ubiquitous cellular transport function which contributes to the regulation of cell pH and of cell volume. However, the only plasma membrane anion exchanger of known identity and sequence is erythroid band 3. Both hybridization and immunologic data support the presence of band 3-related mRNAs and proteins in nonerythroid tissues. We have used low stringency hybridization with the murine band 3 cDNA to clone a band 3-related cDNA from murine kidney and from 70Z/3 pre-B cells. The cDNA encodes a band 3-related protein (B3RP) of 1237 amino acids, with a predicted mass of 137 kDa. The carboxyl-terminal hydrophobic domain of B3RP has an amino acid sequence 67% identical to that of band 3, with a very similar predicted secondary structure. The amino-terminal hydrophilic domain of B3RP has two sections. The section adjacent to the putative membrane-associated segment is 33% identical in amino acid sequence to the amino-terminal, cytoplasmic domain of band 3. The other, far amino-terminal section of B3RP has no correspondent in the band 3 sequence. B3RP mRNA is present in a variety of epithelial and other tissues and probably encodes an anion exchange protein of wide distribution.
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