ACCELERATED EVOLUTION OF TRIMERESURUS-OKINAVENSIS VENOM GLAND PHOSPHOLIPASE A(2) ISOZYME-ENCODING GENES

Three Trimeresurus okinavensis (To; himehabu snake, Crotalinae) venom gland phospholipase A(2) (PLA(2)) isozyme-encoding genes, gPLA(2)-o1, gPLA(2)-o(2) and gPLA(2)-o3, were isolated from its genomic DNA librar y. The nucleotide (nt) sequence analysis revealed that two of the thre e genes (gPLA(2)-o2 and gPLA(2)-o3) occasionally have been converted t o inactivated genes by introduction of one base insertion or substitut ion. It was confirmed from Southern blot analysis that the To haploid genome contains only three venom gland PLA(2) isozyme genes herein iso lated. Comparison of these genes showed that nonsynonymous nt substitu tions have occurred more frequently than synonymous nt substitutions i n the protein-coding regions, except for the signal-peptide coding dom ain, implying that To venom gland PLA(2) isozyme genes have evolved vi a accelerated evolution, Such an evolutionary feature of To venom glan d PLA(2) isozyme genes proves the general universality of accelerated evolution previously drawn for venom gland PLA(2) isozyme genes of oth er crotalinae snakes. The variability in the mature protein-coding reg ions of three To venom gland PLA(2) isozyme genes appears to have been brought about by natural selection for point mutations.