Figure 2: Mechanical displacement of a single nucleosome in the presence of competitor DNA.

(a) Experimental configuration. A single dsDNA molecule was mechanically unzipped using an optical trap (Supplementary Fig. 1A). The dsDNA contained a positioned nucleosome followed by a long naked DNA segment (Supplementary Fig. 2A, Supplementary Table 1 and Methods). Linear competitor dsDNA of 2,987 bp was introduced into the chamber at varying concentrations immediately before mechanical disruption. N=121, 52, 57, 39, 38 and 92 traces for 0, 30, 50, 100, 200 and 300 ng μl⁻¹ competitor DNA concentrations, respectively. (b) Two example unzipping traces in the presence of 100 ng μl⁻¹ of competitor DNA. The top trace shows an absence of a transferred nucleosome to the downstream DNA, whereas the bottom trace shows the presence of a transferred nucleosome. (c) The probability of nucleosome transfer to downstream dsDNA as a function of competitor DNA concentration. Error bars represent 95% confidence intervals (Methods). A direct prediction (not a fit) based on DNA looping and a simple competitive binding relation (Methods) is shown for comparison.