GENOMIC STRUCTURES OF CARDIOTOXIN-4 AND COBROTOXIN FROM NAJA-NAJA ATRA (TAIWAN COBRA)

Two genomic DNAs with the size of 2.3 kb and 2.4 hh, which were isolat ed from the liver of Naja naja atra (Taiwan cobra), encoded the precur sors of cardiotoxin 4 and cobrotoxin, respectively, Both genes shared virtually identical overall organization with three exons separated by two introns, which were inserted in the similar positions of the gene 's coding regions. Moreover, their nucleotide sequences shared approdm ately 84.2% identity. This result reveals the evolutionary relationshi p between cardiotoxin and cobrotoxin. The exon/intron structures of ca rdiotoxin 4 and cobrotoxin genes were similar to that reported for era butoxin c gene, a neurotoxin genomic DNA from a sea snake (Laticauda s emifasciata). However, in contrast to the finding that the intron 2 of these genes had a similar size, a notable variation with the size of intron 1 was observed (1233 bp, 1269 bp and 191 bp for cardiotoxin 4, cobrotoxin and erabutoxin c genes, respectively). The different size w ith intron I is due to the middle region at the first intron of cardio toxin 4 and cobrotoxin genes, which encoded small nucleolar RNA (snonN A), being absent in that of erabutoxin c gene. These results, together with the finding of the potential mobility of snoRNA genes during evo lution, suggest that intron insertions or deletions of snoRNA genes oc cur with the evolutionary divergence of snake neurotoxins and cardioto uins. (C) 1997 Academic Press.