Molecular evolution of toxin genes in Elapidae snakes

The venom of the sea krait, Laticauda semifasciata, consists primarily of two toxic proteins, phospholipase A₂ (PLA₂) and a three-finger-structure toxin. We have cloned both toxic protein genes, including the upstream region. PLA₂ genes contain three types of inserted sequences: an AG-rich region, a chicken repeat 1-like long interspersed nucleotide element sequence and an intron II 3′ side repeat sequence. The molecular divergence of L. semifasciata PLA₂ genes was defined on the basis of the inserted sequences and their sequence homology. The length of intron I in the three-finger-structure toxin genes differs from species to species. The alignment analysis of intron I of the three-finger-structure toxin genes revealed that the intron I sequence of the ancestral gene comprised ten genetic regions. A hypothetical evolutionary process for the three-finger-structure toxin genes has also been developed.