Isolation, sequencing and characterization of two cDNA clones coding for trypsin‐like enzymes from the midgut of Aedes aegypti

In order to understand the regulation of trypsin genes by the blood meal, we constructed a cDNA library from mRNA isolated from midguts of blood-fed female Aedes aegypti. The library was screened with a Drosophila melanogaster trypsin-like gene; twelve cDNAs were isolated and sequenced. Two clones were 846 bp and 788 bp long with 762 bp and 716 bp open reading frames, respectively. The cDNAs were identified as coding for serine proteases by the presence of conserved serine, histidine and aspartic acid residues; the presence of an aspartate residue at position 176 suggests that the clones were derived from trypsin-like gene transcripts rather than chymotrypsin or other serine proteases. One of the clones contained a 5' untranslated region and coding regions for putative signal and activation peptides, suggesting that the product is secreted as an inactive zymogen and processed by autoactivation. Southern analysis of genomic DNA suggests that trypsin is encoded by a multigene family in A. aegypti.