Hemin Control of Globin Synthesis

Human mature erythrocyte postribosomal supernatant contains a hemin-reversible translational repressor of globin synthesis as measured in the rabbit reticulocyte cell-free system. Incubation of human supernatant minus hemin at 37” for 2 hours results in conversion of the repressor to a hemin-irreversible form. The presence of 35 pM hemin retards this conversion. Both hemin-reversible and -irreversible forms of the repressor may be partially purified by precipitation of supernatant at pH 5. Incubation of the partially purified heminreversible repressor minus hemin at 37” for 1 hour or longer results in conversion to the irreversible form. Hemin (35 pM) also retards this conversion. The activity of the repressor is destroyed by incubation with trypsin or by boiling and is therefore presumed to be a protein. Both forms of the repressor are eluted at the same point on a Sephadex G-200 column corresponding to a molecular weight of 3.0 X 105. The isolation of a hemin-reversible translational repressor from an erythroid cell which has lost its protein synthetic capability is evidence that this inhibitor is a physiological regulator of globin synthesis.