Partial characterization of chromosomal proteins tightly bound to chicken erythroid DNA

Extraction of chicken reticulocyte and erythrocyte chromatins with 2 M NaCl yields a small fraction (about 5%) of the total DNA which is very tightly bound to a class of nonhistone chromatin proteins (DNA-P). This DNA fraction has previously been shown to be significantly enriched in active gene sequences. The proteins associated with reticulocyte and erythrocyte DNA-P were analyzed by two-dimensional gel electrophoresis. Reticulocyte DNA-P yield predominantly three major proteins, designated G1, G2, and G3 with relative masses of 80 000, 50 000, and 58 000, respectively. Erythrocyte DNA-P show only two proteins which appear to be similar to the reticulocyte G1 and G2 proteins, except in much reduced quantities as revealed by two-dimensional polyacrylamide gel electrophoresis. Amino acid analysis of the three reticulocyte proteins revealed that the ratio of acidic to basic amino acid residues increased in the order G1 less than G2 less than G3, while the respective isoelectric points also increased in that order.