Molecular analysis of cDNA and the transcript encoding the depressant insect selective neurotoxin of the scorpion Leiurus quinquestriatus hebraeus

Analysis of mRNA transcribed off the gene encoding the depressant insect selective neurotoxin (LqhIT2) of the scorpion Leiurus quinquestriatus hebraues revealed a transcript about 400 nucleotides long and two putative precursors of about 4.4 and 3.5 kb long. Poly(A)⁺ RNA, purified from the venom-gland segments of the scorpion, was reverse transcribed into cDNA and a cDNA library was constructed. Two closely related cDNA clones were isolated from the library by probing with a partial cDNA clone encoding the depressant insect toxin of the scorption Buthotus judaicus. Sequence analysis of the two LqhIT2 cDNA clones revealed an identical 63 bp leader sequence, a 183 bp sequence encoding the mature polypeptide, and 9 bp encoding Gly-Lys-Lys prior to the termination codon. The two clones are distinguished by a single base substitution at the codon corresponding to amino acid residue 16 of the mature toxin, and at the non-coding region preceding the poly(A) tail. These findings elucidate the processing steps in the maturation of LqhIT2 and indicate genetic polymorphism among the genes encoding this toxin.