CHARACTERIZATION OF MAJOR MIDGUT PROTEINASE CDNAS FROM HELICOVERPA-ARMIGERA LARVAE AND CHANGES IN GENE-EXPRESSION IN RESPONSE TO 4 PROTEINASE-INHIBITORS IN THE DIET

A Helicoverpa armigera larval midgut cDNA library from larvae raised o n an artificial, protein-rich, inhibitor-free diet contained very larg e numbers of serine proteinase positive clones, DNA sequencing of six random positive cDNAs and 12 PCR derived products identified trypsin g enes classifiable into three families, and chymotrypsin and elastase g enes classifiable into a single family each, Genomic blots established that the most highly expressed of the trypsin families contained abou t 18 genes, and that the chymotrypsin and elastase families contained about 14 and 2 genes respectively, The levels of mRNA corresponding to the highly expressed trypsin and chymotrypsin families were determine d following chronic ingestion of four proteinase inhibitors, Compared to insects on an inhibitor-free diet, chymotrypsin mRNA was increased by all inhibitors, and trypsin mRNA levels decreased, This occurred in dependent of whether the inhibitor was solely a trypsin inhibitor (apr otinin), an inhibitor of both trypsin and chymotrypsin (proteinase inh ibitor II, soybean trypsin inhibitor) or predominantly a chymotrypsin inhibitor (proteinase inhibitor I), Changing the protein level of the diet did not affect trypsin mRNA levels, but chymotrypsin mRNA levels decreased with increasing dietary protein. (C) 1998 Elsevier Science L td, All rights reserved.