Gene structure, cDNA sequence, and developmental regulation of a low molecular weight hemolymph protein from Locusta migratoria

Abstract

AbstractFrom a Locusta migratoria genomic DNA library, a gene has been isolated that codes for a previously unrecognized hemolymph protein of Mr = 19,000, designated 19k protein. The gene has at least five exons, extending over about 9 kb of DNA. Its polypeptide product, obtained by cell‐free translation of mRNA selected from adult fat body RNA by hybridization with the cloned DNA, is precipitated by antiserum against a low molecular weight hemolymph protein fraction. The mature protein product has been purified from locust hemolymph, and an N‐terminal sequence of 20 amino acids has been determined. In polyacrylamide gel electrophoresis, this protein comigrates with apolipophorin III, from which it was previously not distinguished, but it is clearly distinct by amino acid composition and sequence. The genomic clone was used as a probe to isolate a fat body cDNA clone of the 19k protein mRNA. The 938‐base pair cDNA clone contains a 516‐base pair open reading frame. The deduced 172‐amino acid polypeptide includes an apparent signal peptide, a sequence of four amino acids that may represent a prosegment, and a sequence identical (with a single exception, which may reflect polymorphism) with the N‐terminal sequence of the hemolymph protein. Its mRNA occurs at a low level in late larval fat body, is abundant in the newly eclosed adult, then declines to a low level, and rises again at days 8–10; it is greatly reduced after destruction of the corpora allata with precocene and then is elevated after treatment with methoprene, suggesting stimulation by juvenile hormone. The biological role of 19k protein is unknown.