Figure 1.

A schematic drawing of the closed and open conformations of a nucleosome that originates from the DNA end breathing motion observed at low salt concentrations. The H3 tails are shown as dashed lines and the H4 tails as solid lines (one H4 tail is only partially visible due to the orientation of the nucleosome). A symmetric breathing motion is pictured here, but a possible alternative model exists in which the DNA breathing occurs asymmetrically. In this case, only one of the DNA ends breathes away from the histone core at a time. The circles at the DNA ends depict the locations of the FRET dye pair.