Identification of novel serine proteinase gene transcripts in the midguts of two tropical insect pests, Scirpophaga incertulas (Wk.) and Helicoverpa armigera (Hb.)

We have used RT PCR and 3'RACE to identify diverse serine proteinase genes expressed in the midguts of the rice yellow stem borer (Scirpophaga incertu las) and Asian corn borer (Helicoverpa armigera). The RT-PCR primers encode d the conserved regions around the active site histidine57 and serine195 of Drosophila melanogaster a trypsin, including aspartate189 of the specifici ty pocket. These primers amplified three transcripts (SiP1-3) from midguts of S. incertulas, and two transcripts (HaP1-2) from midguts of H. armigera. The five RT PCR products were sequenced to permit design of gene-specific forward primers for use with anchored oligo dT primers in 3'RACE. Sequencin g of the 3'RACE products indicated that SiP1, SiP2 and HaP1 encoded trypsin -like serine proteinases, while HaP2 encoded a chymotrypsin-like serine -pr oteinases. The SiP3 transcript proved to be an abundant 960 nt mRNA encodin g a trypsin-like protein in which the active site serinel95 was replaced by aspartate. The possible functions of this unusual protein are discussed. ( C) 2000 Elsevier Science Ltd. All rights reserved.