Molecular cloning of the mouse gene coding for carbonic anhydrase IV

Carbonic anhydrase IV (CA IV) is expressed on apical surfaces of renal tubular epithelium and endothelium of specialized capillary beds. It plays a key role in bicarbonate reabsorption in kidney and in CO2 transport in other tissues. The human cDNA and genomic sequences have been cloned and characterized. Here we report the cloning and characterization of the entire mouse CA IV gene (contained in two overlapping lambda clones), which should enable generation of targeting constructs for disrupting the mouse CA IV gene to produce mouse models for in vivo analysis of CA IV gene function. The gene is approximately 8.2 kb long and contains eight exons ranging from 54 to 434 bp in length. The first exon (exon 1a) encodes the signal sequence. Exons 1b through 7 encode the remaining coding sequences. Exon 7 encodes the C terminus of the membrane-associated protein, as well as the 242-bp 3' untranslated sequence. The nucleotide sequence alignment between mouse and rat CA IV cDNAs reveals 84% identity. The nucleotide sequence alignment between mouse and human CA IV shows 69% identity in the coding region and all of the exon-intron boundaries are conserved, as are the sizes of the introns. The corresponding mouse and human exons are similar, except for the length of the untranslated regions in exons 1a and 7 and two small insertion/deletion events in exons 1a and 4. The 5' flanking region of the mouse gene (-300 to -1) is GC rich and contains 16 CpG dinucleotides. A TATA box sequence and several transcription factor binding sequences are identified upstream of exon 1a. Comparison of the nucleotide sequences surrounding the TATA box (-300 to -1) between mouse and human CA IV genes revealed 70% identity, indicating that regulatory sequences are as highly conserved as coding sequences between mouse and human CA IV genes.