Changes in Histone Acetyl Content and in Nuclear Non-Histone Protein Composition of Avian Erythroid Cells at Different Stages of Maturation

Abstract

Duck erythroid cells were fractionated by centrifugation in bovine serum albumin density gradients.Differences in cell density were correlated with the stage of maturation as determined by biochemical and morphological parameters.Avian erythroid cells increase in density as they mature.Cell populations corresponding to known stages in differentiation were compared with regard to histone composition and degree of acetylation, nature and amount of the non-histone nuclear proteins, and DNA and RNA synthetic capacities.Although the total histone to DNA ratio of the chromatin does not vary appreciably during maturation, the relative proportion of the erythroid cell-specific histone F2c increases at least P-fold with the increasing age of the cell, whereas the other histones, except F2a2, decrease.The degree of acetylation of histones F2al and F3 decreases with the increasing age of the cell.The non-histone protein complement of the erythroid cell nucleus decreases 6-fold during maturation.Analysis of the non-histone proteins in polyacrylamide gels containing sodium dodecyl sulfate shows a limited heterogeneity and a remarkable similarity in their electrophoretic patterns at different stages in maturation.Quantitative rather than qualitative changes predominate as maturation proceeds.The decline in non-histone protein content with age is striking particularly in the lower molecular weight components.However, a protein band of molecular weight 55,000 is conserved selectively during maturation and it represents the predominant component of the non-histone nuclear proteins of the mature erythrocyte.The nucleoprotein changes occurring during erythrocyte maturation parallel a decrease in the amount of chromatinassociated RNA and the rate of RNA synthesis.The average RNA synthetic capacity of the isolated erythroblasts and early polychromatic erythrocytes is about 8 times higher than that of the mature erythrocyte fraction.