Characterizing both the regulation of red cell ferritin and iron storage during ontogeny and the relationship of ferritin structure to the availability of iron is crucial to understanding erythroid maturation and the molecular basis of iron storage, as well as to understanding diseases involving abnormal cell maturation and/or iron overload, e.g. thalassemia, leukemia, sickle-cell anemia and hemachromatosis. Red cell iron storage has several unique features such as the dramatic decrease in ferritin concentration and transferrin saturation during ontogeny, iron-stimulated (translationally controlled) red cell ferritin synthesis in mature, embryonic (larval) cells, and the unusual amino acid composition (high serine and glycine) of red cell ferritin. We propose to exploit the unique features of red cell iron storage in our studies on the regulation, structure, and function of red cell ferritin as follows: Regulation - red cell ferritin synthesis will be examined, during ontogeny and erythroid maturation, in relation to (1) transferrin saturation and structure, (2) translational control (effect of hemin, polysome size, termination), (3) transcription (translatable m-RNA content), (4) quantitative changes in red cell histone classes, and (5) regulatory mutations for red cell ferritin which will be sought among strains of anemic mice. Structure and function - will be analyzed by (1) comparing the primary structure of red cell and liver ferritin with particular emphasis on phosphorylated peptides, (2) characterizing the iron-protein interface in ferritin using extended x-ray fine structure (EXAFS) analysis, (3) comparing iron release in in vitro from natural and chemically modified red cell and liver ferritin and Imferon, (4) characterizing red cell ferritin in human diseases.