Transcriptional induction of diverse midgut trypsins in larval Agrotis ipsilon and Helicoverpa zea feeding on the soybean trypsin inhibitor.
Midgut trypsins insensitive to inhibition by the soybean trypsin inhibitor (STI) were found to be transcriptionally regulated in A. ipsilon and H. zea larvae feeding on STI, as demonstrated by injections with actinomycin, a transcriptional inhibitor, which abolished the production of these STI-insensitive trypsins. The induced, STI-insensitive trypsins differed from the constitutive, STI-sensitive trypsins in their susceptibility to inhibitors based on sizes, suggesting that the induced enzymes limited access to their active site by blocking bulky inhibitors. Twenty midgut cDNA fragments(1) were amplified using trypsin-specific PCR primers and at least twelve were shown to encode structurally diverse trypsins. High sequence diversity was observed for both the enzymes encoded by STI-induced mRNAs and those from larvae that had not been exposed to STI. Northern blots showed that midgut mRNAs hybridizing to various trypsin cDNA probes were either transcribed de novo or up-regulated following ingestion of STI. Southern hybridizations indicated the presence of multiple trypsin gene families in the insect genomes. The complete sequence of a trypsin gene(1) from A. ipsilon (AiT9) revealed the presence of three introns. Comparison of 5' upstream sequences(1) from AiT9 and AiT6 genes from A. ipsilon revealed putative TATA box and disparate regulatory motifs, within 500 bp of each translational start site.
Mazumdar-Leighton
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Department of Entomology, Cornell University, New York State Agricultural Experiment Station, Geneva, NY 14456, USA. sm90@nysaes.cornell.edu
Broadway
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015139:Blotting, Southern; D018076:DNA, Complementary; D004064:Digestive System; D005091:Exons; D005247:Feeding Behavior; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D007438:Introns; D007814:Larva; D008969:Molecular Sequence Data; D009036:Moths / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D011110:Polymorphism, Genetic; D012333:RNA, Messenger; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic; D014357:Trypsin / Q000096:biosynthesis / Q000235:genetics*; D014360:Trypsin Inhibitor, Kunitz Soybean / Q000494:pharmacology*; D014361:Trypsin Inhibitors / Q000494:pharmacology*
D018076:DNA, Complementary; D012333:RNA, Messenger; D014361:Trypsin Inhibitors; D014360:Trypsin Inhibitor, Kunitz Soybean; D014357:Trypsin