Variant chicken kidney AE1 anion exchanger transcripts are derived from a single promoter by alternative splicing

Previous studies have demonstrated that three variant transcripts, AE1-3, AE1-4 and AE1-5, are derived from the AE1 gene in chicken kidney. These variant transcripts encode AE1 anion exchangers that possess alternative N-terminal cytoplasmic domains. To determine the mechanisms involved in generating these transcripts, a genomic clone, containing the unique sequences at the 5' ends of the AE1-4 and AE1-5 transcripts, was isolated. Characterization of this clone revealed that the sequences at the 5' ends of the AE1-3, AE1-4 and AE1-5 transcripts were each present with an approx. 1.2-kb BamHI fragment of the chicken AE1 gene. RNA blotting and RNase protection analyses using probes derived from this genomic clone have shown that the AE1-4 variant corresponds to the approx. 4.5-kb chicken kidney AE1 transcript, while the AE1-5 variant corresponds to the approx. 5.1-kb transcript. These studies have shown that the AE1-5 transcript extends further 5' than had been previously shown from cDNA cloning studies, and contains the sequence present at the 5' end of the AE1-4 transcript. In addition, primer extension analyses have shown that the variant kidney AE1 transcripts initiate transcription from a common site. This result indicates that the expression of the AE1-3, AE1-4, and AE1-5 transcripts is regulated by a single promoter, P3, that is distinct from the P1 and P2 erythroid-specific promoters of the chicken AE1 gene.