Lipoxygenase mRNA in rabbit reticulocytes. Its isolation, characterization and translational repression

The synthesis of the erythroid lipoxygenase, an enzyme which is of importance for the degradation of mitochondria during the maturation of reticulocytes to erythrocytes, was studied in reticulocytes from bone marrow and in density-separated fractions from peripheral blood of anemic rabbits. Lipoxygenase mRNA was enriched to about 75% by digestion of polysomes with protease K, poly(U)-Sepharose chromatography and repeated sucrose gradient centrifugation. From sucrose gradient centrifugation, electrophoresis and electron microscopy a molecular weight of about 10(6) was calculated. Synthesis of lipoxygenase is absent in erythroblasts, in very young reticulocytes obtained from bone marrow, or in the lightest fractions of reticulocytes from the peripheral blood. More mature blood reticulocytes show a considerable synthesis of the enzyme. The induction of the synthesis of the lipoxygenase seems to be initiated when reticulocytes have reached the peripheral blood. It is shown that lipoxygenase mRNA is present in reticulocytes as a translationally inactive free cytoplasmic messenger ribonucleoprotein (mRNP) particle. After deproteinization isolated mRNA obtained from masked mRNP codes for authentic lipoxygenase in a cell-free protein-synthesizing system of reticulocytes.