Primary structure of the rat kidney band 3 anion exchange protein deduced from a cDNA

A rat kidney cDNA library was screened using an oligonucleotide hybridization probe derived from an amino acid sequence of the mouse erythrocyte Band 3 Cl-/HCO3- exchanger. Ten cDNAs representing a single class of mRNA and encoding the kidney Band 3 anion exchanger were isolated. Analysis of the deduced amino acid sequence revealed that kidney Band 3 is a truncated version of erythrocyte Band 3. The 848-amino acid rat kidney protein is virtually identical to mouse erythrocyte Band 3 except that it lacks the first 79 amino acids of the N-terminal cytoplasmic domain. Exons 1, 2, and 3 of the Band 3 gene, which are included in erythrocyte Band 3 mRNA, are not present in the kidney cDNA. The 5'-untranslated regions of kidney Band 3 transcripts contain sequences from the third intron and exons 4 and 5 of the Band 3 gene. The sequences from exons 4 and 5 that serve as untranslated sequences in the rat kidney mRNA have the potential to encode amino acids 46-79 of erythrocyte Band 3 but are not part of an open reading frame; the apparent translation initiation site corresponds to codon 80 of mouse erythrocyte Band 3 mRNA. Northern blot hybridization studies indicate that two additional Band 3 mRNAs, which differ in size from the major 4.5-kilobase pair transcript in kidney, are expressed at low levels in kidney and brain.