Symmetric immobile DNA branched junctions.

Branch migration is an isomerization of Holliday recombination intermediates that arises from their homologous (2-fold) sequence symmetry. This isomerization relocates the branch point in an apparently random fashion and thereby complicates the study of the physical and structural properties of these structures. For the past decade, these properties have been studied in low-symmetry immobile junctions, whose sequence asymmetry eliminates branch migration. The asymmetric findings of many of these studies suggest the need for a system combining both immobility and symmetry. Double-crossover DNA molecules have been used to create molecules with both these properties. Immobility is achieved by flanking one crossover with a symmetric junction and the other crossover with an asymmetric junction. Close torsional coupling between the two junctions renders the symmetric junction immobile. These molecules will enable the characterization of thermodynamic, structural, dynamic, liganding, and substrate properties of symmetric branched DNA molecules in a sequence-specific fashion.