FIGURE 5.

Neighboring nucleosomes enhance nucleosome stability. A, shown is the effect of increasing magnesium concentration on nucleosome stability. Mono-, di-, tri-, and tetranucleosomal arrays were incubated in the presence of 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, 2.0,, and 2.5 were incubated in the corresponding mm concentrations of MgCl₂. Arrowheads indicate the position of free DNA for each nucleosomal length tested. B, shown is the effect of nucleosome density on nucleosome stability. Trinucleosomal arrays, varying in degree of saturation, were created by ligating combinations of mononucleosomes and free DNA to create trinucleosomal DNA templates with one, two, or three octamers assembled as shown in the schematic, left. Lanes 1–3 show arrays with trinucleosomal DNA template and one, two, or three assembled octamers, respectively. Each array was incubated in the presence or absence of 2.0 mm MgCl₂ then run on a native 4% polyacrylamide gel and stained with ethidium bromide. Arrowheads indicate the position of free trinucleosomal DNA.