DNA may seem an unlikely molecule from which to build nanostructures, but this is not correct. The specificity of interaction that enables DNA to function so successfully as genetic material also enables its use as a smart molecule for construction on the nanoscale. The key to using DNA for this purpose is the design of stable branched molecules, which expand its ability to interact specifically with other nucleic acid molecules. The same interactions used by genetic engineers can be used to make cohesive interactions with other DNA molecules that lead to a variety of new species. Branched DNA molecules are easy to design, and the can assume a variety of structural motifs. These can be used for purposes both of specific construction, such as polyhedra, and for the assembly of topological targets. A variety of two-dimensional periodic arrays with specific patterns have been made. DNA nanomechanical devices have been built with a series of different triggers, small molecules, nucleic acid molecules and proteins. Recently, progress has been made in self-replication of DNA nano-constructs, and in the scaffolding of other species into DNA arrangements.

The synthesis of DNA/nylon ladder oligomers is described. Three stages of the development are addressed: the synthesis of 2'-beta-substituted phosphoramidites, the deprotection/purification protocols of ODNs modified with both amino and carboxyl groups, and amide bond-forming reactions on the ODNs. The established technology and the novel DNA-based ladder oligomer structure opens a pathway to the synthesis of topological molecular objects and networks templated by DNA through versatile DNA nanotechnology. The DNA-based ladder oligomers may find application in the antisense area.

DNA tensegrity triangles self-assemble into rhombohedral three-dimensional crystals via sticky ended cohesion. Crystals containing two-nucleotide (nt) sticky ends (GA:TC) have been reported previously, and those crystals diffracted to 4.9 Å at beam line NSLS-I-X25. Here, we analyze the effect of varying sticky end lengths and sequences, as well as the impact of 5’- and 3’-phosphates on crystal formation and resolution. Tensegrity triangle motifs having 1-, 2- and 3-nt sticky ends all form crystals. X-ray diffraction data from the same beam line reveal that the crystal resolution for a 1-nt sticky end (G:C) and a 3-nt sticky end (GAT:ATC) were 3.4 Å and 4.2 Å respectively. Resolutions were determined from complete data sets in each case. We also conducted trials that examined every possible combination of 1-nucleotide and 2-nucleotide sticky-ended phosphorylated strands and successfully crystallized all 16 possible combinations of strands. We observed the position of the 5’-phosphate on either the crossover (1), helical (2), or central strand (3) affected the resolution of the self-assembled crystals for the 2-turn monomer (3.0 Å for 1–2P-3P) and 2-turn dimer sticky ended (4.1 Å for 1–2-3P) systems. We have also examined the impact of the identity of the base flanking the sticky ends, as well as the use of 3’-sticky ends. We conclude that crystal resolution is not a simple consequence of the thermodynamics of the direct nucleotide pairing interactions involved in molecular cohesion in this system.

We extend the generality of nucleic acid-based structural nanotechnology by incorporating non-natural nucleic acids into a DNA double crossover (DX) molecule; visualizing two-dimensional arrays of these DX molecules by Atomic Force Microscopy (AFM) enables us to measure the helical repeat of any heteroduplex sequence capable of forming the outer arms of a DX.

We have determined the 1.50 Å crystal structure of the DNA decamer, d(CCACNVKGCGTGG) (CNVK, 3-cyanovinylcarbazole), which forms a G-quadruplex structure in the presence of Ba2+. The structure contains several unique features including a bulged nucleotide and the first crystal structure observation of a C-tetrad. The structure reveals that water molecules mediate contacts between the divalent cations and the C-tetrad, allowing Ba2+ ions to occupy adjacent steps in the central ion channel. One ordered Mg2+ facilitates 3′-3′ stacking of two quadruplexes in the asymmetric unit, while the bulged nucleotide mediates crystal contacts. Despite the high diffraction limit, the first four nucleotides including the CNVK nucleoside are disordered though they are still involved in crystal packing. This work suggests that the bulky hydrophobic groups may locally influence the formation of non-Watson–Crick structures from otherwise complementary sequences. These observations lead to the intriguing possibility that certain types of DNA damage may act as modulators of G-quadruplex formation.