Gene structure and polymorphism. Of an invertebrate nitric oxide synthase gene

Nitric oxide synthases (NOSs) are ubiquitous in living organisms. However, little is known about the evolution of this large gene family. The first in ducible NOS to be described from an invertebrate regulates malaria parasite (Plasmodium spp.) development in the mosquito Anopheles stephensi. This si ngle copy gene shows the highest homology to the vertebrate neuronal isofor ms, followed by decreasing homology to endothelial and inducible isoforms. The open reading frame of 1247 amino acids is encoded by 19 exons, which sp an approximate to 33 kilobases. More than 50% of the mosquito exons, distri buted around the putative heme, calmodulin, and FAD/NADPH cofactor-binding domains, are conserved with those of the three human genes. Repetitive elem ents identified within the larger introns include a polymorphic dinucleotid e repeat, two tandem repeats, and a putative miniature inverted repeat tran sposable element. Sequence analysis and primer extension indicate that the upstream promoter is 'TATA-less' with multiple transcription start sites wi thin approximate to 250 base pairs of the initiation methionine. Transcript ion factor binding sites in the 5'-flanking sequence demonstrate a bipartit e distribution of lipopolysaccharide- and inflammatory cytokine-responsive elements that is strikingly similar to that described for vertebrate induci ble NOS gene promoters. (C) 1999 Elsevier Science B.V. All rights reserved.