α-Neurotoxin gene expression in Naja sputatrix: identification of a silencer element in the promoter region

Alpha-neurotoxin (α-NTX) from the venom of cobra, Naja sputatrix, is a highly lethal post-synaptic toxin that is responsible for the lethality caused by the venom. However, this toxin is found at low levels (3%) in the crude venom. The expression of its gene is determined by a promoter which is 90% similar to the promoter of another three-fingered toxin, cardiotoxin (CTX), which is produced in large amounts (60%) in the same venom. Functional analysis of the NTX-2 gene promoter demonstrated the presence of a silencer element of 24 nucleotides (nt −678 to −655) at its 5′ flanking region. This element has been found to play a major role in the down-regulation of NTX-2 gene expression. A point mutation on this silencer appears to attenuate its repressive property in CTX-2 gene.