Comparative analysis of gene expression mechanisms between group IA and IB phospholipase A2 genes from sea snake Laticauda semifasciata.

Phospholipase A(2) (PLA(2)) genes expressed in the venom glands of the sea snake, Laticauda semifasciata, were investigated. Both mRNAs, encoding group IA (without a pancreatic loop) and group IB (with pancreatic loop), were detected from venom glands by Northern blot hybridization analysis and RT-PCR. The results of quantitative PCR analysis indicated that the expression amount of group IA genes was around 100-300 times greater than that of group IB genes. Sequence analysis of 5'-upstream regions and a reporter gene assay of the genes (groups IA and IB) previously cloned showed that the functional sequence (411 bp) was inserted in the 5'-flanking region of the group IA PLA(2) genes. It seemed that the contribution of the inserted sequence to the amount of transcribed mRNAs was greater than that of number of genes present in the genome. Comparative analysis of the 5'-flanking sequences from several snake genes encoding toxic PLA(2)s revealed that this sequence was probably inserted into an ancestral gene of PLA(2) with a pancreatic loop. After the duplication of the gene, which contained the inserted sequence, the PLA(2) gene without a pancreatic loop evolved from one of the duplicate genes. This inserted sequence might determine the future of the genes expressed in the venom glands.