The Finding of a Group IIE Phospholipase A(2) Gene in a Specified Segment of Protobothrops flavoviridis Genome and Its Possible Evolutionary Relationship to Group IIA Phospholipase A(2) Genes

The genes encoding group IIE phospholipase A(2), abbreviated as IIE PLA(2), and its 5' and 3' flanking regions of Crotalinae snakes such as Protobothrops flavoviridis, P. tokarensis, P. elegans, and Ovophis okinavensis, were found and sequenced. The genes consisted of four exons and three introns and coded for 22 or 24 amino acid residues of the signal peptides and 134 amino acid residues of the mature proteins. These IIE PLA(2)s show high similarity to those from mammals and Colubridae snakes. The high expression level of IIE PLA(2)s in Crotalinae venom glands suggests that they should work as venomous proteins. The blast analysis indicated that the gene encoding OTUD3, which is ovarian tumor domain-containing protein 3, is located in the 3' downstream of IIE PLA(2) gene. Moreover, a group IIA PLA(2) gene was found in the 5' upstream of IIE PLA(2) gene linked to the OTUD3 gene (OTUD3) in the P. flavoviridis genome. It became evident that the specified arrangement of IIA PLA(2) gene, IIE PLA(2) gene, and OTUD3 in this order is common in the genomes of humans to snakes. The present finding that the genes encoding various secretory PLA(2)s form a cluster in the genomes of humans to birds is closely related to the previous finding that six venom PLA(2) isozyme genes are densely clustered in the so-called NIS-1 fragment of the P. flavoviridis genome. It is also suggested that venom IIA PLA(2) genes may be evolutionarily derived from the IIE PLA(2) gene.