title: Divergence of genes encoding B chains of beta-bungarotoxins.
abstract: The structural organization of the genes encoding B2, B4, B5 and B6 chains of beta-bungarotoxins are reported in this study. These genes shared virtually identical overall organization with three exons interrupted by two introns in similar positions. On the contrary, intron 1 of these genes had a similar size, a notable variation with the size of intron 2 was observed. It was found that two regions at the second intron of B1 and B2 chains were absent in that of B4, B5 and B6 chains. RT-PCR analyses indicated that Bungarus multicinctus venom gland, heart, liver and muscle expressed the RNA transcripts showing sequence similarity with the intronic segment being deleted in B4, B5 and B6 chain genes. This reflects that the ancestral gene of the intronic segment might insert in multiple loci of B. multicinctus genome. Comparative analyses of B chain genes showed that the protein-coding regions of the exons are more diverse than introns, except for in the signal peptide domain. These results suggest that intron insertions or deletions occur with the evolution of B chains, and that accelerated evolution may diversify the protein-coding sequence of B chain genes same as snake phospholipase A2, neurotoxin and cardiotoxin genes.
authors.affiliation: Institute of Biomedical Sciences, National Sun Yat-Sen University, Kaohsiung 804, Taiwan, ROC.
authors.forename: Yun-Ching
authors.initials: YC
authors.lastname: Cheng
authors.forename: Ku-Chung
authors.initials: KC
authors.lastname: Chen
authors.forename: Shu-Kai
authors.initials: SK
authors.lastname: Lin
authors.forename: Long-Sen
authors.initials: LS
authors.lastname: Chang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002038:Bungarotoxins / Q000737:chemistry* / Q000235:genetics; D017838:Bungarus; D004247:DNA / Q000737:chemistry; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D019143:Evolution, Molecular; D015723:Gene Library; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship
chemical_list: D002038:Bungarotoxins; D017931:DNA Primers; D004247:DNA