April 2005

Nanotechnology

New publications, experiments, and breakthroughs--and what they mean

By Monya Baker (edit)

Molecular Manufacturing
A machine built out of DNA

Context: Deep in every cell, miniature biological machines called ribosomes forge proteins. Following instructions written in our genetic code, ribosomes weld together amino acids to form the enzymes that modulate body chemistry and the structural materials, like collagen, that hold the body together. As good as engineers are at building machines and structures on the scale of people, they have few tools for building on the scale of molecules, as a ribosome does.

Researchers from New York University have taken a landmark step toward the goal of imitating the ribosome, building a programmable, nanoscale machine that can weld together DNA molecules.

Methods and Results: NYU chemists Shiping Liao and Nadrian Seeman twisted and bent DNA to build a structure that is approximately 110 nanometers long, 30 nanometers high, and 2 nanometers thick, roughly the same size as a ribosome, though not as complex. Just as the ribosome can be programmed to weld amino acids together in a prescribed sequence, this DNA machine can be instructed to select specific small molecules of DNA for concatenation. The DNA machine can swivel into four geometric positions and can be locked into any one of them by another fragment of DNA, the "instructions." Locking the machine into position dials in the sequence of very short DNA strands that it will recognize and position for welding. The welding itself is performed by an enzyme that links DNA molecules. In the absence of the machine, this enzyme would create many different combinations of DNA strands; in its presence, only a single, preprogrammed combination results.

Why it Matters: The evolution of the ribosome transformed terrestrial biology, enabling cells to manufacture any protein of any size or shape as needed. Nanotechnologists seek a similar watershed, the development of a machine that could make improved pharmaceuticals or biomaterials. Liao and Seeman's approach could also be extended to the manufacture of nonbiological products, with the goal of producing materials that are impossible to construct using conventional chemistry. Measured against these ambitions, their current nanodevice appears crude, but it is likely to be followed by more sophisticated successors.

Source: Liao, S., and N. C. Seeman. 2004. Translation of DNA signals into polymer assembly instructions, Science 306:2072–2074.