Comparison of the Larval Serum Proteins of Drosophila melanogaster

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Abstract
Immunological data, amino acid composition, and coordinate control during development suggest that the α, β and γ subunits of the major protein of Drosophila larval serum (LSP-1) are coded for by genes which evolved by replications of an ancestral gene followed by mutation. In order to test this hypothesis, and to study the relationship of these genes with that coding for the second major larval serum protein (LSP-2), we compared the one and two-dimensional peptide maps of all four larval serum protein subunits. One-dimensional maps generated by three different proteases showed many similarities among these proteins. Two-dimensional peptide mapping of the methionine-containing tryptic peptides showed that half of these peptides are common to all four larval serum protein subunits, and that about two-thirds are common to the three LSP-1 subunits. These observations show that the LSP-1 subunits are more closely related to each other than any is to LSP-2, and supported the initial suggestion that the proteins are homologous. Because the genes for the LSP-1 subunits are each located on a different chromosome, the LSP-1 subunits are a suitable system for investigating the evolution and dispersal of related genes, and trans control in eukaryotes.