Figure 5.

YOYO-1-induced untwisting. (a) Measurement scheme. Torsionally constraint but relaxed DNA is destained by adding 1 M NaCl, which causes negative supercoiling of the destained DNA. Subsequently, positive turns are added until the DNA is becoming relaxed again. (b) Supercoiling curves measured at a force of 0.25±0.03 pN in 10 mM phosphate buffer for YOYO–DNA (filled green circles), YOYO–DNA after partial stepwise (filled gray circles) and complete destaining (filled black circles). The shift of the supercoiling curves is accompanied by a linear decrease of the DNA length (orange dashed line). (c) Shift of the torsionally relaxed position plotted over the resulting contour length decrease (filled black circles). A linear fit (solid orange line) to the data provides a slope of 0.13±0.01 turns nm⁻¹.