During their final maturation, nondividing chicken erythrocytes undergo heterochromatinization and decline of RNA synthesis. Upon incubation of the maturing erythrocytes in vitro with [14C]leucine, the chromosome-bound histone and nonhistone proteins become highly labeled. Chromatographic analysis of acid-extractable chromosomal proteins revealed that these cells synthesize the arginine-rich but not the lysine-rich or slightly lysine-rich histones. Tryptic peptide map analysis of the radioactive proteins showed that the labeled amino acid was incorporated into the chromosome-specific polypeptide chains. The results demonstrate that the synthesis of chromosomal nonhistone proteins and of arginine-rich histones can proceed without concurrent DNA synthesis. We propose that the chromosomal proteins which are synthesized during erythrocyte maturation may be involved in heterochromatinization and associated gene repression.
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