Figure 10.

Proposed model of the high-salt type 1 solution, which consists of a mixture of duplex DNA and DNA Holliday junction structures. The part of the model shown in the orange box is a classic example of static heterogeneity. The interconversion between duplex DNA and DNA Holliday junctions is a macroscopic structural change that takes place on the timescale of minutes, thus establishing a steady-state mixture of components. We propose to expand this depiction of the high-salt type 1 solution with the addition of the structures shown in the gray box, which account for dynamic heterogeneity. Dynamic heterogeneity is present in these solutions via DNA “breathing”, a local structural change that takes place on a hundreds of μs timescale. These structural changes are proposed to explain the presence of small subpopulations of long-lived adjacent dimers and monomers in the solution, as exemplified by the structures labeled “restricted bubble” and “extended bubble”, respectively.