Genomic cloning and promoter analysis of a mouse anion exchanger 3 (AE3) gene

The brain and cardiac isoforms of anion exchanger 3 (AE3) are considered to use their own promoters for their expression. However, little is known as to how the alternative transcription initiation is regulated. As a first step for elucidating the regulation, we obtained a genomic gene of mouse AE3. The 19-kbp clone contains about 6 kbp of 5' flanking region, 23 exons, and 22 introns. We have sequenced the whole region including introns and determined the intron-exon boundaries. Six amino acids are different from those deduced from the reported mouse AE3 cDNA. We measured a promoter activity of the 5' flanking region of the exon 1 for a brain type isoform and that of the exon C1 for a cardiac type isoform. The upstream region of the exon C1 indeed showed a promoter activity in rat cardiomyoblastic H9C2 cells, rat pheochromocyotoma PC12 cells, and human HeLa cells whereas the 5' flanking region of the exon 1 does not in HeLa cells, suggesting that the promoter for the cardiac type is rather ubiquitously active.