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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.

The synthesis of two storage protein subunits, 76,000-Mr and 82,000-Mr polypeptides, by the testes sheath has been studied in Heliothis virescens. Like fat body, which is the primary site of synthesis for the large extratesticular pool, cells of the testes sheath secrete glycosylated storage proteins assembled into hexamers. The testis sheath differed from fat body in several important respects, including the failure to synthesize an abundant (in the hemolymph) 74,000-Mr storage protein, its relatively reduced expression of the 76,000-Mr polypeptide, and the absence of resorption of storage proteins from the lumen of the testis during pupal development. Cyst cells were also shown to import actively the 82,000-Mr storage protein by pinocytosis of testicular fluid and transfer it to the developing spermatids. Unlike other cell types that sequester storage proteins in the form of cytoplasmic granules, their localization within spermatids was exclusively mitochondrial. These observations suggest that expression of the storage protein genes is regulated tissue specifically and reveal novel pathways for their transport and, perhaps, utilization and function during development.

Fifteen unique chorion protein-encoding cDNAs from gypsy moth have been completely sequenced. These sequences are encoded by a family of genes, based on pairwise similarity values of 78-100% within a 225-nt region. Pairwise comparisons and maximum parsimony analysis strongly support the existence of two clusters of 11 and four sequences each, called noc1 and noc2. While noc2 consists of two subclusters, there is little character support for subclusters within noc1. The highly localized character-state distribution on the parsimony tree in gypsy moth is reminiscent of that in Bombyx mori, specifically for those chorion families that have been shown to undergo gene conversion. Gene conversion thus becomes a reasonable explanation for the homogeneity of noc1 sequences and for their distinctness from noc2. The relationship between the two major clusters of chorion sequences in gypsy moth (noc1, noc2) and Bombyx mori (Bm alpha, Bm beta) has been addressed through mixed-species tree construction. All four groups cluster separately, thus providing no direct evidence of orthologous sequences. However, the occurrence of gene conversion could have eliminated such evidence. The relationship between the chorion gene tree and the species cladogenic event is discussed, as are biases in codon usage, base composition, and nucleotide transformations.