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DNA folds into octahedron COURTESY OF MICHAEL PIQUE While DNA can be used to make rigid nanoscaffolding, the topologies of 3-D geometric DNA objects have prevented polymerases from copying them, making it difficult to scale up production of the molecules via cloning. Now, William M. Shih, Joel D. Quispe, and Gerald F. Joyce from Scripps Research Institute report the design and synthesis of an easily cloned, 1,669-nucleotide, single-stranded DNA molecule that folds into an octahedron in the presence of five 40-nucleotide strands of DNA [Nature, 427, 618 (2004)]. The octahedron measures 22 nm across. (Reconstruction from cryo-electron microscopy is shown; colors indicate relative electron density.) Each of the octahedron's edges is made of pairs of double helices arranged in a side-by-side manner. Shih designed the DNA object so that seven of the edges would form by paranemic cohesion, in which internal loops from the long strand wrap around one another to make a bridge without actually making or breaking any covalent bonds. Double crossovers, which resemble two double helices exchanging strands at two positions, form the other five edges via association between the long and short strands. |
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