Genetic characterization of the mRNAs encoding alpha-bungarotoxin: isoforms and RNA editing in Bungarus multicinctus gland cells.

The mRNA encoding alpha-bungarotoxin (alpha-Butx) was prepared from the venom glands of Bungarus multicinctus by Cap-finder cDNA synthesis. The sequences of the 3'- and 5'-flanking regions including a signal peptide of alpha-Butx were almost identical with those of Elapidae and Hydrophiidae toxins, suggesting that they may have the same origin. Sixteen polymorphic mRNA sequences of alpha-Butx were detected from B.multicinctus gland cells. Analysis of the genomic DNA of alpha-Butx indicated that the polymorphic mRNA originated from one DNA sequence. Most of the mutations in alpha-Butx mRNA were silent and the hot-spot variations occurred at 78, 107, 129, 198 and 201 nt in alpha-Butx mRNA. Ten distinct protein sequences of alpha-Butx could be deduced from the polymorphic mRNA and one of the isoforms has already been isolated. Since alpha-Butx DNA is a single copy in the genome, the RNA polymorphism might result from post-transcriptional editing. These results indicate that the authentic alpha-Butx is in fact derived from edited mRNAs. RNA editing may contribute a common mechanism toward the diversity of alpha-neurotoxins in snake glands.