A phospholipase A(2)-like pseudogene retaining the highly conserved introns of mojave toxin and other snake venom group II PLA(2)s, but having different exons

Mojave toxin is a neurotoxic, heterodimeric phospholipase A(2) (PLA(2)) from the venom of the Mojave rattlesnake (Crotalus scutulatus scutulatus) and is characteristic of all rattlesnake presynaptic neurotoxins, Here, we describe a phospholipase A(2) pseudogene (psi-Mtx) located 2,000 nucleotides upstream, and on the opposite DNA strand, from a gene for Mojave toxin acidic subunit (Mtx-a), The pseudogene lacks the first exon and a few segments of noncoding DNA found in functional snake venom PLA(2) genes, but does have the coding information for a complete PLA(2) protein, psi-Mtx retains the unusual gene sequence similarity pattern found in functional viperid PLA(2) genes, When compared to genes from C. s. scutulatus and the Habu snake (Trimeresurus flavoviridus), psi-Mtx shows strong conservation of nocoding regions and variable protein-coding regions, Although the nocoding regions of psi-Mtx are conserved with respect to other viperid PLA(2) genes, the three exons code for a unique PLA(2)-like protein similar in sequence to ammodytoxin b found in the venom of the western sand viper (Vipera ammodytes ammodytes), The structure of these genes suggests a common ancestor for all viperid PLA(2) genes, Phylogenetic analysis of psi-Mtx, Mtx-a, Mtx-b, pgPLA 1a, and pgPLA 1b suggest that psi-Mtx diverged from an ancestral sequence before the presumed gene duplication event leading to Mtx-a and Mtx-b, However, analysis of the basis of coding regions alone gives a conflicting result.