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 polypept ides ranging in size from similar to 95 to 112 kDa in chicken kidney. To determine the origin of this diversity, we have cloned and characte rized the kidney AE1 anion exchangers. These studies have shown that t he 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 an d AE1-5 transcripts encode predicted polypeptides of similar to 94 kDa , which are identical to the erythroid AE1-1 anion exchanger except fo r the absence of the 78 NH2-terminal amino acids of the AE1-1 polypept ide. In contrast, the AE 1-4 transcript encodes a predicted polypeptid e 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 AE 1-4 transcripts are generated by alternative splicing of a single prim ary transcript, while DNA blotting analyses have shown that the putati ve transcription initiation sites of the variant AE1-4 and AE1-5 trans cripts lie several kilobases downstream of the transcription initiatio n sites of the erythroid AEL-1 and AE1-2 transcripts. These results su ggest that the pattern of accumulation of the variant kidney AE1 anion exchangers is regulated by a complex pattern of alternative transcrip tional initiation and differential RNA splicing.