Isolation of human aquaporin-CD gene

The human gene encoding aquaporin-CD (AQP-CD) was isolated, and its structural organization was characterized. The gene appeared to exist as a single copy in the human genome and comprises four exons distributing over 5 kilobases. The size range of exons is 81-761 base pairs, and that for introns is approximately 3000 to approximately 250 base pairs. The exon-intron boundaries of human AQP-CD gene are identified at identical positions in other related genes, the human AQP-CHIP gene and the human major intrinsic protein gene. The major transcription initiation sites were identified to positions 93 and 94 base pairs upstream of the ATG initiation codon by primer extension and ribonuclease protection assay. The 5'-flanking region of the hAQP-CD gene was characterized by a TATA box, two GATA consensus sequences, an AP-1 site, an AP-2 site, three E-boxes, and a cyclic AMP-responsive element. These structural features will lead to a better understanding of the mechanisms of tissue-specific expression and the regulation by dehydration in AQP-CD gene and will also be of help in search for possible genetic disorders in human AQP-CD gene.