MANDUCA-SEXTA HEMOLYMPH FERRITIN - CDNA SEQUENCE AND MESSENGER-RNA EXPRESSION

A cDNA clone encoding a subunit of the tobacco hornworm Manduca sexta (Ms) hemolymph (serum) ferritin (Fer) has been identified and sequence d. The deduced amino acid (aa) sequence shows approx. 50% similarity t o vertebrate Fer subunit sequences, and the nucleotide sequence contai ns a stem-loop structure in the 5' untranslated region that could serv e as an iron-responsive element (IRE). The stem-loop of this putative IRE exhibits high identity to vertebrate IRE that play an essential ro le in the control of Fer synthesis. The Ms Fer subunit lacks one of th e three Tyr residues required for the rapid biomineralization of iron shown in vertebrate heavy-chain Fer. In addition, aa residues that com prise the putative ferroxidase centers generally are not conserved, su ggesting that the Ms Fer subunit more closely resembles the vertebrate light-chain subunit. Northern blot analyses indicate that the fer mRN A is expressed in the midgut, fat body and hemocytes, with the greates t expression in the midgut.