Bov-B long interspersed repeated DNA (LINE) sequences are present in Vipera ammodytes phospholipase A(2) genes and in genomes of Viperidae snakes

Ammodytin L is a myotoxic Ser49 phospholipase A(2) (PLA(2)) homologue, which is tissue-specifically expressed in the venom glands of Vipera ammodytes. The complete DNA sequence of the gene and its 5' and 3' nanking regions has been determined. The gene consists of five exons separated by four introns, Comparative analysis of the ammodytin L and ammodytoxin C genes shows that all intron and flanking sequences are considerably more conserved (93-97%) than the mature protein-ceding exons. The pattern of nucleotide substitutions in protein-coding exons is not random but occurs preferentially on the first and the second positions of codons, which suggests positive Darwinian evolution for a new function. An Ruminantia specific ART-2 retroposon, recently recognised as a 5'-truncated Bov-B long interspersed repeated DNA (LINE) sequence, tvas identified in the fourth intron of both genes, This result suggests that ammodytin L and ammodytoxin C genes are derived by duplication of a common ancestral gene. The phylogenetic distribution of Bov-B LINE amen vertebrate classes shows that, besides the Ruminantia, it is limited to Viperidae snakes (Vipera ammodytes, Vipera palaestinae, Echis coloratus, Bothrops alternatus, Trimeresurus flavoviridis and Trimeresurus gramineus). The copy number of the 3' end of Bov-B LINE in the Vipera ammodytes genome is between 62000 and 75000, The absence of Bov-B LINE at orthologous positions in other snake PLA(2) genes indicates that its retrotransposition in the V. ammodytes PLA(2) gene locus has occurred quite recently, about 5 My ago. The amplification of Bov-B LINEs in snakes may have occurred before the divergence of the Viperinae and Crotalinae subfamilies. Due to its wide distribution In Viperidae snakes it may be a valuable phylogenetic marker. The neighbor-joining phylogenetic tree shows two clusters of truncated Bov-B LINE, a Bovidae and a snake cluster, indicating an early horizontal transfer of this transposable element.