Chromatin fragments containing bovine 1.715 g ml-1 satellite DNA. Nucleosome structure and protein composition

Some of the properties of chromatographically purified satellite chromatin are compared with those of unfractionated, control chromatin. Nucleosomes were present in the purified satellite chromatin as verified by digestion with micrococcal nuclease and DNase I and by electron microscopy. Average nucleosome DNA repeat lengths of 186 +/- 7 and 193 +/- 5 base pairs were obtained through micrococcal nuclease digestion of the purified satellite chromatin and control chromatin, respectively; nucleosome spacer lengths were equally heterogeneous for the two chromatin samples. The distribution of Eco RI-produced chromatin fragments of different size in the satellite chromatin was the same as that calculated assuming random cleavage at each Eco RI site, consistent with the notion that nucleosomes do not have specific locations on the 1.715 g ml-1 satellite DNA. The purified satellite chromatin contained little non-histone protein, but did contain all five histones and all detectable histone sequence variants. Amounts of the core histones were identical in the satellite chromatin and the control chromatin, but the amount of histone H1 was 30% less in the satellite chromatin than in the control. Although the molar ratios for the major sequence variants of both histones H3 and H2A differed between kidney and thymus, the ratios were the same for satellite and control chromatin isolated from a single tissue.