Identification and molecular analysis of storage proteins from Heliothis virescens.

Three abundant storage proteins have been detected in larval and pupal hemolymph and pupal fat body of the tobacco budworm, Heliothis virescens. These polypeptides have subunit molecular weights of 74,000, 76,000, and 82,000, as determined by SDS-PAGE and exist as 450,000-Mr hexamers in their native state. A purified 82,000-Mr storage protein fraction has been obtained along with a preparation containing equivalent amounts of the 74,000-Mr and 76,000-Mr subunits, and antisera raised to each of these components have been used to document the developmental profiles of protein accumulation and synthesis by fat body. cDNA clones corresponding to each of three abundant classes of fat body mRNAs have been recovered, and at least one of these has been unambiguously demonstrated to encode the 82,000-Mr storage protein subunit. Northern blot studies with these cDNA clones revealed that the developmental accumulation of transcripts in fat body for each was consistent with the general pattern of storage protein biosynthesis, and more interestingly, that transcripts hybridizing to two of these cDNA sequences are also found in tests. These two cDNAs have also been sequenced revealing that one encodes a polypeptide similar to arylphorins, a class of storage proteins widely distributed in Insecta. The derived amino sequence of the second cDNA, corresponding to the 82,000-Mr protein, had no unusual compositional features and determination of its structural relationship to other hemolymph polypeptides awaits molecular analysis of related genes from other insects.