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 scutul atus) 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 gen e for Mojave toxin acidic subunit (Mtx-a), The pseudogene lacks the fi rst exon and a few segments of noncoding DNA found in functional snake venom PLA(2) genes, but does have the coding information for a comple te PLA(2) protein, psi-Mtx retains the unusual gene sequence similarit y pattern found in functional viperid PLA(2) genes, When compared to g enes from C. s. scutulatus and the Habu snake (Trimeresurus flavovirid us), psi-Mtx shows strong conservation of nocoding regions and variabl e 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 ammodyto xin b found in the venom of the western sand viper (Vipera ammodytes a mmodytes), The structure of these genes suggests a common ancestor for all viperid PLA(2) genes, Phylogenetic analysis of psi-Mtx, Mtx-a, Mt x-b, pgPLA 1a, and pgPLA 1b suggest that psi-Mtx diverged from an ance stral sequence before the presumed gene duplication event leading to M tx-a and Mtx-b, However, analysis of the basis of coding regions alone gives a conflicting result.