STRUCTURE AND EXPRESSION OF THE GENE FOR THE PROTHORACICOTROPIC HORMONE OF THE SILKMOTH BOMBYX-MORI

We cloned and characterized two allelic variants of the gene for the B ombyx mori prothoracicotropic hormone (PTTH), a homodimeric 30-kDa bra in secretory protein. These PTTH genes contain five exons that encode a precursor protein consisting of 224 amino acid residues whose C-term inal 109 residues represent the PTTH subunit. The Bombyx haploid genom e contains a single copy of the PTTH gene. The major site of PTTH expr ession is the brain but expression at a very low level occurs in the g ut. One Bombyx brain at day 0 of the fifth larval instar contained 2.4 -2.8 pg PTTH mRNA, and this amount did not change markedly during larv al-pupal development.