An additional promoter functions in the human aldolase A gene, but not in rat

The aldolase A gene was isolated from a human DNA library, mapped and sequenced. This gene comprises 12 exons and spans 6.5 kb. From the genomic DNA sequence and from the previous sequence analysis of the cDNA, it was revealed that the first exon L1 and the second exon encode the 5' non-coding sequence of mRNA L1, while the third and forth exons (corresponding to exons M and L2) encode different mRNA, mRNA M and L2, respectively; the following eight exons (exons 5-12) are shared commonly by all the mRNA species. These results indicate that the mRNA species are generated from a single aldolase A gene from one of exons L1, M or L2, in addition to exons 5-12, and also that the usage of a leader exon is similar but clearly distinct from that of rat aldolase A gene which we analyzed [Joh, K., Arai, Y., Mukai, T. & Hori, K. (1986) J. Mol. Biol. 190, 401-410]. By comparing the promoter regions in the human and rat aldolase A genes, we found similar sequences in the rat genome corresponding to those of the human L1, M and L2 promoter. We could not, however, detect any transcripts starting from sequences corresponding to the human L1 promoter in the rat genome, although the products corresponding to human M and L2 were detected. Thus, we conclude that the L1 promoter was either acquired by the human genome or deleted from the rat genome after human and rat diverged during evolution.