Logo: University of Southern California

Nadrian Seeman

DNA: Not Merely the Secret of Life

Nadrian Seeman - New York University


Our laboratory works in the area of structural DNA nanotechnology. We use the concept of reciprocal exchange between DNA double helices to produce branched DNA motifs, like Holliday junctions, or related structures, such as double crossover (DX), triple crossover (TX), paranemic crossover (PX) and DNA parallelogram motifs. We combine DNA
motifs, using sticky-ended cohesion, to produce specific structures. The key strength of sticky-ended cohesion is that it produces predictable adhesion combined with known structure. We have constructed DNA stick-polyhedra, whose edges are double helices, and whose vertices are the branch points of DNA branched junctions. These include a cube, a truncated octahedron, and an irregular graph.

Nanorobotics are key to the success of nanotechnology. We have used two DX molecules to construct a DNA nanomechanical device by linking them with a segment that can be switched between left-handed Z-DNA with right-handed B-DNA. PX DNA has been used to produce a robust sequence-dependent device that changes states by varied hybridization topology. The sequence-dependent nature of this device means that a variety of them attached to a motif can all be addressed individually. Recently, we have used this device to make a machine that does chemical translation.

A central goal of DNA nanotechnology is the self-assembly of periodic matter. We have constructed micron-sized 2-dimensional DNA arrays from DX, TX, two kinds of parallelogram motifs. We can produce specific designed patterns visible in the AFM from DX and TX molecules. We can change the patterns by changing the components, and by modification after assembly. Recently, we have used new motifs to produce honeycomb-shaped arrays. The key structural challenge in the area is the extension of the 2D results obtained so far to 3D systems with a high degree of ordering. Crystals with dimensions as large as a millimeter, ordered to 10 Å resolution (as determined by X-ray diffraction) have been produced. Ultimately, we expect to be able to produce high resolution crystals of DNA host lattices with heterologous guests, leading to well-ordered bio-macromolecular systems amenable to diffraction analysis. Other challenges are to incorporate DNA nanomechanical devices in periodic and aperiodic lattices and to use the
lattices to organize nanoelectronic components, such as metallic nanoparticles or carbon nanotubes.

Nadrian C. Seeman was born in Chicago in 1945. Following a BS in biochemistry from the University of Chicago, he received his Ph.D. in biological crystallography from the University of Pittsburgh in 1970. His postdoctoral training, at Columbia and MIT, emphasized nucleic acid crystallography. He obtained his first independent position at
SUNY/Albany, where his frustrations with the macromolecular crystallization experiment and his awareness of the fatal series--no crystals, no crystallography, no crystallographer--led him to the campus pub one day in the fall of 1980. There, he realized that the similarity between 6-arm DNA branched junctions and the flying fish in the periodic array of Escher's 'Depth' might lead to a rational approach to the organization of matter on the nanometer scale, particularly crystallization. Ever since, he has been trying to implement this approach and its spin-offs, such as nanorobotics and the organization of nanoelectronics; since 1988 he has worked at New York University. When told in the mid-1980's that he was doing nanotechnology, his response was similar to that of M. Jourdain, the title character of Moliere's Bourgeois Gentilehomme, who was delighted to discover that he had been speaking prose all his life. Further information is available at http://seemanlab4.chem.nyu.edu.