Fig. 7
From: An affinity-structure database of helix-turn-helix: DNA complexes with a universal coordinate system
Mirror symmetry of DNA molecules. For any two canonical matching regions in different DNA molecules there are two possible alignments due to the mirror symmetry of DNA. a The strands F1 and R1 are mapped to F2 and R2, respectively (mapping between F1 and F2 is depicted by dashed lines). b The F2/R2 DNA molecule is rotated 180° around the horizontal axis, which results in strands F1 and R1 being mapped to strands R2 and F2, respectively. Schematic representations of the mappings between strands are shown on the right. Note that both alignments preserve the 5′ → 3′ directionality of DNA, i.e. alignments in which the mapped regions run in opposite directions are not allowed