Structure and chromosomal localization of the gene for crotamine, a toxin from the South American rattlesnake, Crotalus durissus terrificus

Abstract

Crotamine is a 42 amino acid-long basic polypeptide, one of the major components of the South American rattlesnake, Crotalus durissus terrificus , venom. The mRNA has about 340 nucleotides and codifies a pre-crotamine, including the signalpeptide, the mature crotamine, and a final lysine. In this report, we describe the crotamine gene with 1.8 kb organized into threeexons separated by a long phase-1 (900 bp) and a short phase-2 (140 bp) introns. Exon 1 includes the 5 0 -untranslated region andcodifies the first 19 amino acids of the signal peptide. Exon 2 codifies 42 amino acids, three belonging to the signal peptide and39 to the mature crotamine. Exon 3 codifies the last three amino acids of the mature toxin and the terminal lysine. The crotaminegene was mapped by in situ hybridization to the end of the long arm of chromosome 2, the intensity of signals differing betweenthe two homologues. This may reflect a difference in gene copy numbers between chromosomes, a possible explanation for thevariable amounts of crotamine found in the venom.