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.
Mitochondrial transcription factor A (TFAM) is the primary component necessary for transcription initiation of mitochondrial DNA (mtDNA). TFAM has been recently shown to package mtDNA without ...sequence specificity and to be essential for mtDNA maintenance. To further understand TFAM functions in development and ageing, human and Drosophila TFAM-ΔC which lack C-terminal 25 amino acids necessary for the transcription initiation were expressed in D. melanogaster by GAL4/ UAS system. When the two kinds of TFAM-ΔC were expressed by the Actin-Gal4 driver at 25℃ and 28℃, only flies possessing human TFAM-ΔC were obtained at 25℃. When their lifespan was examined at 28℃, it significantly reduced. These suggest that an excess of TFAM-ΔC extremely lower viability during development and that TFAM may be involved in ageing. In contrast, when expression of TFAM-ΔC was induced by the hs-Gal4 driver, flies were viable at 25℃ for both human and Drosophila TFAM-ΔC. The amount of mtDNA surprisingly increased to about 8-fold of controls when they were maintained at 25℃ or 3O℃ for 5 days after eclosion. Examination of their lifespan is now in progress.
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