Devices with DNA software may one day be fitted into cells.
DNA has problem-solving power.
"If you wear the right glasses, a lot of what you see inside the cell is computation," says Ehud Shapiro of the Weizmann Institute in Rehovot, Israel. Now Shapiro and his colleagues have turned the computational power of biological molecules to their own ends1.
The researchers have built a machine that solves mathematical problems using DNA as software and enzymes as hardware. A trillion such biomolecular machines - working at more than 99.8% accuracy - can fit into a drop of water.
Cut and paste
The new molecular computers input is a DNA strand. Its letters represent a string of binary symbols - ones and zeroes. The machine answers questions such as whether the input contains an even number of ones.
The computers hardware is two enzymes. One cuts the DNA strands when it recognizes a specific sequence of letters, another sticks DNA snippets back together again. The cutting enzyme makes incisions a few bases shy of its recognition sequence. So its cuts create a range of different DNA molecules, depending on what surrounds the recognition site.
The researchers program each problem by designing DNA software molecules that bind only to a subset of the slices of input DNA. Each software molecule contains a recognition site for the cutting enzyme, and some other DNA letters that determine where on the shortened input molecule the next cut occurs.
The enzymes chomp their way along an input molecule until the calculation is complete - like an early computer processing data encoded on a paper tape. Finally, the joining enzyme attaches one of two output DNA molecules, ending the sequence of reactions and representing the answer to the initial question - yes or no, for example.
"It works better than anything Ive seen, by far," comments Eric Baum, a computer scientist at the NEC Research Institute, Princeton, New Jersey. Baum is sceptical whether DNA computers will ever become useful. "But this is a step in the right direction," he says.
JOHN WHITFIELD | © Nature News Service
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