No abstract

The structure and organization of the genes encoding the long-chain neurotoxins and four other isoforms of weak neurotoxins in the venom of Naja sputatrix are reported. The genes contained three exons interrupted by two introns, a structure similar to other members of the three-¢nger toxin family. The proteins encoded by these genes, however, show varied af¢nity towards nicotinic acetylcholine receptors. Phylogenetic analysis of these genes showed that the weak neurotoxin gene is con¢ned to a distinct group. We also observe that speci¢c mutations of the gene provide the diversity in function in these toxins while maintaining a common structural sca¡old. This forms the ¢rst report where the molecular basis of evolution of postsynaptic neurotoxins from an ancestral gene can be demonstrated using the same species of snake.