Structure and chromosomal localization of the human constitutive endothelial nitric oxide synthase gene

Endothelial nitric oxide (NO) synthase is a unique NO synthase isoform that is expressed constitutively by vascular endothelium both in vivo and in vitro and is believed essential to local vascular homeostasis. This calcium/calmodulin-dependent isoform is distinct from neuronal NO synthase. Genomic clones encoding the human endothelial NO synthase were isolated and the structural organization of the gene was determined. The gene contains 26 exons spanning approximately 21 kilobases of genomic DNA, encodes a messenger RNA of 4052 nucleotides, and is present as a single copy in the haploid human genome. Characterization of 5'-flanking genomic regions indicates that the endothelial NO synthase promoter is "TATA-less" and exhibits proximal promoter elements consistent with a constitutively expressed gene that is found in endothelial cells, namely Sp1 and GATA motifs. The 5'-flanking region contains putative AP-1, AP-2, NF-1, heavy metal, acute-phase response shear stress, and sterol-regulatory cis-elements. The human endothelial NO synthase gene was assigned to the 7q35-->7q36 region of chromosome 7 by Southern blot hybridization of human-rodent somatic cell hybrid lines and fluorescence in situ hybridization, whereas human neuronal NO synthase localized to the 12q24.2 region of chromosome 12.