CLONING AND CHARACTERIZATION OF THE CDNAS ENCODING NA-SPECIFIC TOXIN-1 AND TOXIN-2 OF THE SCORPION CENTRUROIDES-NOXIUS HOFFMANN( CHANNEL)

Using a cDNA library prepared from venomous glands of the Mexican scor pion Centruroides noxius Hoffmann the genes that encode toxins 1 and 2 were identified, cloned and sequenced. In view of the proposed mechan ism for processing the mature peptides coded by these two genes, the c orresponding peptide-toxins were sequenced de novo. Mass spectrometric and H-1-NMR analyses of the C-terminal peptide produced by enzymatic digestion of both toxins indicated that the last residue is serine-ami de. Sequence comparison revealed that these two genes have a similarit y of 56% and 80% at the amino acid and nucleotide levels, respectively . Small corrections to the published primary structures were introduce d: Cn toxin 1 has an extra serine residue at position 65 and the resid ue in position 60 is a proline, while the amino acids at positions 34 and 35 of Cn 2 are, respectively, tyrosine and glycine. Sequence compa rison of toxins from the genus Centruroides suggests the presence of a t least three classes of distinct peptides in these venoms.