Gene Analysis for the Prothoracicotropic Hormone of the Silkmoth, Bombyx mori.

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Gene analyses have been made for the prothoracicotropic hormone(PTTH) and a PTTH-like, insulin-related paptide, Bombyxin, of the silkmoth bombyx mori.1) A cDNA encoding PTTH has been cloned from a cDNA expression library derived from the Bombyx brain using a monoclonal antibody against a synthetic fragment of PTTH. The 106-amino acid sequence was deduced from the coding region of this cDNA. It was concluded that PTTH is a homodimer in which the two 106-amino acid peptides are connected together by disulfide bonds. Two genomic DNA clones encoding PTTH was also cloned.2) Using the synthetic oligonucleotides corresponding to the A- and B-chains of bombyxin, the bombyxin cDNAs and genes have been isolated. Bombyxins are first synthesized as a precursor protein,perprobombyxin, whose structure is signal peptid/B-chain/C-peptide/A-chain. This domain organization is the same as in preproinsulins. Multiple bombyxin gene copies exist in the Bombyx genome. Twentyseven copies have been characterized. They are organized in such a characteristicway that two genes form a pair and the genes in each pair are divergently transcribed.3) Six bombyxin-like genes have been isolated from another moth Samia cynthia ricini. Their structure and organization in the genomo are very similar to those of Bombyx bombyxin genes.4) In situ hybridization showed that bombyxin genes are expressed spacifically in the four pairs of mid-dorsal neurosecretory cells of Bombyx brain.