Molecular cloning of cDNA and genomic DNA for human 25-hydroxyvitamin D₃ 1α-hydroxylase

The 25-hydroxyvitamin D₃ 1α-hydroxylase (1α-hydroxylase) is a cytochrome P450 enzyme that catalyzes the conversion of 25-hydroxyvitamin D₃ to 1α,25-dihydroxyvitamin D₃. This enzyme plays an important role in calcium homeostasis. Here we report the molecular cloning of cDNA and gene for human 1α-hydroxylase. The cDNA clone was obtained from a human kidney cDNA library by cross-hybridization with a previously cloned rat cDNA probe. The cDNA consists of 2469 bp and encodes a protein of 508 amino acids that shows 82.5% sequence identity with the rat enzyme. A computer-aided homology search revealed that 1α-hydroxylase shares a relatively high homology with vitamin D₃ 25-hydroxylase (about 40% amino acid identity). Northern blot analysis showed that the 2.5-kb mRNA is most abundant in kidney. The gene for human 1α-hydroxylase spans approximately 6 kb, is composed of nine exons, and is present as a single copy. This molecular cloning makes it possible to investigate the genetic mechanism of diseases related to calcium metabolism, including vitamin D-dependency rickets type I.