cDNA cloning and tissue distribution of mRNAs for two proteins that are related to the band 3 Cl-/HCO3- exchanger.

Abstract

Complementary DNAs encoding two proteins that are related to the Band 3 Cl-/HCO3- exchanger, designated B3RP2 and B3RP3, have been isolated from rat stomach, brain, and kidney libraries. B3RP2 is 1234 amino acids in length and has an Mr of 136,644. B3RP3 is 1227 amino acids in length and has an Mr of 135,405. B3RP2 and B3RP3 exhibit 52 and 50% amino acid identity to Band 3, respectively, and 56% identity to each other. The N-terminal cytoplasmic regions of B3RP2 and B3RP3, which span about 700 amino acids, are more extensive than that of Band 3. The C-terminal hydrophobic regions of the three proteins exhibit a high degree of amino acid identity (64-69%) and have very similar hydropathy profiles, suggesting that they have the same transmembrane organization. The tissue distribution of mRNAs encoding B3RP2, B3RP3, and the Band 3 Cl-/HCO3- exchanger were examined by Northern blot hybridization using poly(A)+ RNAs from a broad range of muscle and non-muscle tissues and from sections of the gastrointestinal tract. B3RP2 mRNAs are expressed in all tissues examined. The highest levels, which include at least three different transcripts, occur in stomach. B3RP3 mRNAs, which also consist of several different transcripts, have a more limited tissue distribution. The highest levels occur in heart, and in gastrointestinal sections the highest levels are in the forestomach. Band 3 mRNAs were observed in many tissues but high levels of expression occurred only in spleen and kidney. Five Band 3 transcripts, ranging in size from 3.6 to 4.9 kilobases, were detected, including three that are expressed in heart.