Figure 1: Mechanical displacement of a single nucleosome.
(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). (b) A representative unzipping trace. A force rise from the naked DNA baseline indicated the detection of a bound protein complex. A dashed vertical line indicates the dyad location of a nucleosome. N=121 traces. (c) Histogram of nucleosome transfer distance. A transfer distance was obtained from the first transfer event of each trace. The histogram was obtained by pooling data from 121 traces. The prediction (not a fit) from the DNA looping model is plotted for comparison. The resulting Pearson test gives a reduced χ2 of 0.53 with a P value of 0.81 (Methods; Supplementary Fig. 4A).
