Ribosome alterations during red cell differentiation

Abstract

Some physical properties and functional aspects of ribosomes from chicken red cells at different stages of maturation have been studied. Ribosomes from chicken embryos, as well as phenylhydrazine-treated and normal adults, were isolated. Sucrose gradient centrifugation analysis and sedimentation velocity determinations showed the presence of polysomes and monosomes in ribosomal preparations from immature cells and only monosomes in preparations from mature cells. In vitro incubation of the red cells with labeled amino acids resulted in high labeling of the polysomes and none or very little of the monosomes. Cesium chloride banding experiments showed many bands for the immature cell ribosomes covering a range from a density of 1.560–1.690 gm/ml. In contrast, while bands from mature cell ribosomes spanned the same total density range, they were fewer in number and were absent from the medium range of 1.590–1.660 gm/ml. Determinations of the sedimentation coefficients in the analytical ultracentrifuge indicated a distinct difference between the S value for monosomes from immature cells (82 average) and the corresponding value from mature cells (62 average). Experiments using synthetic mixtures of isolated monosomes from both cell types confirmed this difference. A model for an in vivo mechanism to account for the rapid disappearance of the ribosomes at the maturation of the red cell is proposed.