The mouse carbonic anhydrase I gene contains two tissue-specific promoters

We report the isolation and characterization of the mouse carbonic anhydrase I (CAI) gene. Direct RNA sequence analysis of the 5' nontranslated regions of CAI mRNA from mouse colon and mouse erythroleukemia cells demonstrated tissue specificity in the lengths and sequences of CAI transcripts. Analysis of several mouse CAI genomic clones showed that the transcripts arose from a single CAI gene with two tissue-specific promoters and eight exons. CAI transcripts in the colon were found to initiate just upstream of the erythroid exon 2 of the CAI gene region sequence. Erythroid transcripts originated from a novel promoter upstream of exon 1, which was located more than 10 but less than 250 kilobases upstream of exon 2. Erythroid exon 1 contained only a nontranslated sequence, which was spliced to exon 2 via a cryptic splice acceptor site located in the region that encoded the colon mRNA 5' nontranslated sequence. The remaining exon-intron junctions were conserved in comparison with those of the CAII and CAIII genes.