Synthesis of chromosomal proteins during the maturation of chicken erythrocytes

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.