Postsynaptic alpha-neurotoxin gene of the spitting cobra, Naja naja sputatrix: Structure, organization, and phylogenetic analysis

The venom of the spitting cobra, Naja naja sputatrix contains highly potent alpha-neurotoxins (NTXs) in addition to phospholipase A(2) (PLA(2)) and ca rdiotoxin (CTX). In this study, we report the complete characterization of three genes that are responsible for the synthesis of three isoforms of alp ha-NTX in the venom of a single spitting cobra. DNA amplification by long-d istance polymerase chain reaction (LD-PCR] and genome walking have provided information on the gene structure including their promoter and 5' and 3' U TRs. Each NTX isoform is similar to 4 kb in size and contains three exons a nd two introns. The sequence homology among these isoforms was Found to be 99%. Two possible transcription sites were identified by primer extension a nalysis and they corresponded to the adenine (A) nucleotide at positions +1 and -45. The promoter also contains two TATA boxes and a CCAAT box. Putati ve binding sites For transcriptional factors AP-2 and GATA are also present . The high percentage of similarity observed among the NTX gene isoforms of N. n. sputatrix as well as with the alpha-NTX and kappa-NTX genes from oth er land snakes suggests that the NTX gene has probably evolved From a commo n ancestral gene.