VARIANT CHICKEN AE1 ANION-EXCHANGERS POSSESS DIVERGENT NH2-TERMINAL CYTOPLASMIC DOMAINS

Immunoblotting analyses have demonstrated that antibodies specific for the chicken erythroid AE1 anion exchanger recognize multiple polypeptides ranging in size from similar to 95 to 112 kDa in chicken kidney. To determine the origin of this diversity, we have cloned and characterized the kidney AE1 anion exchangers. These studies have shown that the kidney AE1 polypeptides are encoded by at least three transcripts, AE1-3, AE1-4, and AE1-5, which differ from the erythroid AE1-1 and AE1-2 transcripts in the sequences present at their 5'-ends, The AE1-3 and AE1-5 transcripts encode predicted polypeptides of similar to 94 kDa, which are identical to the erythroid AE1-1 anion exchanger except for the absence of the 78 NH2-terminal amino acids of the AE1-1 polypeptide. In contrast, the AE 1-4 transcript encodes a predicted polypeptide of similar to 101 kDa, whose 21 NH2-terminal amino acids are unique. Characterization of the AE1 cDNAs has suggested that the AE1-3 and AE1-4 transcripts are generated by alternative splicing of a single primary transcript, while DNA blotting analyses have shown that the putative transcription initiation sites of the variant AE1-4 and AE1-5 transcripts lie several kilobases downstream of the transcription initiation sites of the erythroid AEL-1 and AE1-2 transcripts. These results suggest that the pattern of accumulation of the variant kidney AE1 anion exchangers is regulated by a complex pattern of alternative transcriptional initiation and differential RNA splicing.