Polymorphic cDNAs encode for the methionine-rich storage protein from Manduca sexta

By cDNA cloning and sequencing we have shown that Manduca sexta larvae produce three very closely related methionine-rich storage proteins, MMR1, MMR2 and MMR3. Out of 2256 nucleotides in the coding region, the cDNAs differ by at most twenty-one bases and this leads to a single amino acid difference between MMR1 and MMR2, and between MMR2 and MMR3, whereas MMR1 and MMR3 differ by two amino acids. Using both distance and parsimony methods, similarities between the M. sexta and Bombyx mori methionine-rich and arylphorin storage proteins were examined. Homologous proteins from the two species tend to be more closely related than are the two classes of storage proteins in a single species.