Molecular cloning of Soli E2: an elastase-like serine proteinase from the imported red fire ant (Solenopsis invicta)

The 4th instar larva of the imported red fire ant, Solenopsis invicta, possesses several serine proteinases, one of which, referred to as Soli E2, has been found to contain elastase-like activity. A cDNA library was constructed in lambda gt10 using Poly(A)+RNA from these larvae and a synthetic degenerate oligonucleotide probe corresponding to a sequence encoding the N-terminal of Soli E2 was utilized to screen the library. Two clones were obtained covering the entire coding region of Soli E2, and the predicted structure of this proteinase indicated that it was synthesized as a preproenzyme of 249 amino acids, which was cleaved to give the mature form of 226 residues. In addition, both clones showed identity to the N-terminal amino acid sequence obtained from Edman degradation of the mature purified proteinase. Significantly, Northern blot analysis of the different developmental stages revealed that Soli E2 was selectively expressed in the 4th instar larvae.