FIG. 1.

(a) Schematic of a DNA braid under torsional stress, showing coexistence of straight and plectonemically buckled states. The individual dsDNAs are able to swivel around their contact with the wall, keeping the dsDNAs from twisting. (b) Two duplex DNAs (dark and gray shaded) helically braided in a right-handed manner on the surface of a cylinder of radius R oriented parallel to the ẑ-axis, viewed from two angles. The orthonormal triad (t̂_io, t̂_i⊥r, t̂_i⊥θ), where i ∈ {1, 2} is shown for one of the curves. t̂_1o is in the direction of the tangent to the helix, t̂_1⊥r is oriented radially inward, and t̂_1⊥θ ≡ t̂_1o × t̂_1⊥r. The projection of the triad on the ẑ axis is a constant dependent on the helix parameters (Eq. 3).