Characterisation of the helicostatin peptide precursor gene from Helicoverpa armigera (Lepidoptera : Noctuidae)

The gene encoding the helicostatin peptide family was isolated from a Helic overpa armigera genomic DNA library, The deduced precursor sequence allowed unambiguous identification of all helicostatin peptides and verified the s equences of eight peptides previously isolated. The gene consists of at lea st three exons and encodes a precursor of 225 amino acids that contains thr ee blocks of tandemly arranged helicostatin peptides including seven copies of the C-terminal sequence -YXFGL followed by a single Gly residue for car boxylamidation. Complete endoproteolytic processing at all possible dibasic cleavage sites would generate the seven helicostatin octapeptides previous ly purified from larval extracts. If processing was not complete at the thi rd pair of basic amino acids the octadecapeptide (helicostatin IIa) would a lso be released. Two novel putative helicostatin peptide sequences were ide ntified; YSKFNFGL and ERDMHRFSFGL, both of which had the C-terminal pentape ptide -FXFGL in place of the more usual -YXFGL sequence. Comparison of the helicostatin precursor with that of the cockroaches, locust and flies revea led variation in size, sequence and organisation of the 'allatostatin' prec ursors across different insect orders. In situ hybridisation histochemistry established that helicostatins are expressed in neurones of the central ne rvous system and endocrine cells of the midgut, indicating that the helicos tatins are true brain-gut peptides. Northern blot analysis identified a sin gle transcript of 1.6 kb in mRNA from whole larvae, isolated central nervou s system and gut tissue. (C) 1999 Elsevier Science Ltd. All rights reserved .