Figure 1.

Tethered particle motion experiment investigating the specific interaction between Cre recombinase and loxP sites. (A) Control experiment: the histogram of the BM amplitude was obtained using 1267 bp DNA molecules without loxP sites. The average BM value peaks at 81.6 ± 8.6 nm (n = 53). (B) A histogram of the BM amplitude obtained from 1267 bp DNA molecules without a loxP site after a 1-h incubation with 200 nM Cre recombinase. The histogram was fitted to a two-Gaussian distribution that represented two conditions, in which the centers of the peaks occur at BM values of 81.2 ± 9.6 nm and 62.9 ± 11.5 nm for naked DNA and Cre-bound DNA, respectively (n = 53). (C) The change in the BM amplitude of a single 1267 bp DNA molecule without a loxP site in response to the addition of Cre recombinase. The dashed line indicates the addition of Cre recombinase. (D) Control experiment: the histogram of the BM amplitude was obtained using 1267 bp DNA molecules containing one loxP site. The average BM value peaks at 80.5 ± 12.0 nm (n = 85). (E) A histogram of the BM amplitude obtained from 1267 bp DNA molecules containing one loxP site after 1-h incubation with 200 nM Cre recombinase. The histogram was fitted to a two-Gaussian distribution that represented two conditions, in which the centers of the peaks occur at BM values of 80.5 ± 12.5 and 58.3 ± 9.4 nm for naked DNA and Cre-bound DNA, respectively (n = 85). (F) The change in the BM amplitude of a single 1267 bp DNA molecule containing one loxP site in response to the addition of Cre recombinase. The dashed line indicates the addition of Cre recombinase. The cartoons shown below illustrate the experimental procedure. The white ball represents the streptavidin-labeled 200 nm polystyrene bead, the white spots represent the Cre recombinase molecules, the black curve represents the DNA molecules, the dashed arrowed line represents the Brownian motion amplitude, and the white line represents the loxP sequence. The error is the 95% CL.