FIGURE 6.

Neighboring nucleosomes enhance intermolecular compaction. A, shown is the presence of detergent enhances nucleosome stability. Mono-, di-, tri-, and tetranucleosomal arrays were incubated in the presence of 0.1% Triton X-100 and increasing concentrations of MgCl₂, then run on a native 4% polyacrylamide gel and stained with ethidium bromide. Lanes 0, 0.5, 1.0, 1.5, and 2.0 were incubated in the corresponding mm concentrations of MgCl₂. Arrowheads indicate the position of free DNA for each nucleosomal length tested. B, increasing nucleosomal array length enhances intermolecular compaction. Left, mono-, di-, tri-, and tetranucleosomal arrays were incubated in the presence of 0.1% Triton X-100 and 6.0 mm MgCl₂, then run on a native 4% polyacrylamide gel and stained with ethidium bromide. Lanes 1–4 show mono-, di-, tri-, and tetranucleosomal arrays, respectively. Right, a representative self-association plot of mono, di-, tri-, and tetranucleosomal arrays is shown. Nucleosomes were incubated with 0.1% Triton X-100 and increasing concentrations of MgCl₂. The fraction of nucleosome remaining in the supernatant is plotted as a function of the array concentration.