Similarity of chromatin from different tissues

DNA-protein complex was extracted from a variety of sources and the accessibility of the phosphate groups of the DNA determined by the addition of polylysine; excess unbound polylysine was estimated by its reaction with methyl orange. In chromatin from the livers of normal rats and from rats treated with dimethylnitrosamine, in calf thymus nucleohistone and in avian erythrocyte chromatin, 42 to 47% of the DNA phosphate groups are available for binding polylysine, whereas about 23% of those in DNA-protamine from fish sperm are accessible; however, in the latter case, the free DNA phosphate groups occur only in very small stretches. The binding of polylysine to the chromatin protein carboxyl groups was shown to be negligible. On addition of DNase I to hen erythrocyte chromatin, oligonucleotides and protein are released concurrently, as found previously for rat thymus chromatin (Itzhaki, 1971b). This suggests that in both types of chromatin the DNA is associated extensively with protein, though not fully neutralized. It is concluded that chromatin extracted from very diverse sources is structurally similar, despite large differences in non-histone protein content. © 1973.