Figure 6. Motif Generation.

(a) The Process of Reciprocal Exchange. A red strand and a blue strand exchange to form a red-blue strand and a blue-red strand. (b) Motifs used in Structural DNA Nanotechnology. Two reciprocal exchanges between strands of opposite polarity yield the DX molecule shown. The 'D' means that there are two double helices. The DX+J (a DX combined with a junction) motif, usually made with the extra helix roughly perpendicular to the plane of the other two, is made by combining a DNA hairpin and a DX molecule. The TX (indicating three fused double helices) motif results from combining the DX molecule with another double helix. The PX (standing for paranemic crossover DNA) motif is derived by performing reciprocal exchange between two helices at all possible positions where strands of the same polarity come together. The JX₂ (indicating a PX with two juxtaposed backbone groups) motif is similar to the PX motif, except that reciprocal exchange is omitted at two adjacent juxtapositions.