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mrz
18-08-03, 22:22
First game-playing DNA computer revealed
09:52 18 August 03
NewScientist.com news service

The first game-playing DNA computer has been revealed - an enzyme-powered tic-tac-toe machine that cannot be beaten.

The human player makes his or her moves by dropping DNA into 3 by 3 square of wells that make up the board. The device then uses a complex mixture of DNA enzymes to determine where it should place its nought or cross, and signals its move with a green glow.

The device, dubbed MAYA, was developed by Milan Stojanovic, at Columbia University in New York, and Darko Stefanovic, at the University of New Mexico in Albuquerque. Kobi Benenson, who works on other DNA approaches at the Weizmann Institute in Israel, says the work demonstrates the most complex use of molecules as logic gates to date, and "represents a significant advance in DNA computing."

More complex computational tasks than noughts and crosses could be tackled with different arrangements of the enzymes. But the pair acknowledge that the approach will never rival silicon computers, because human action is needed to operate the gates in system and it is not reusable.

"It's lovely work," says Peter Bentley, a computer scientist linked to University College London. But he notes that a system that cannot be extended much further than playing tic-tac-toe "is merely a novelty". Stojanovic and Stefanovic are aware of this and are now focusing on developing simple decision-making solutions that can operate in vivo. Molecules could, for example, assess faults in a living cell and then either kill or repair it.


Snip apart


In previous DNA computing schemes, all of the elements are mixed in a test tube and the answer to the calculation is deduced from the product of the reaction. MAYA is the first interactive system. The nine wells occupy just one square centimetre and each contain mixtures of the enzymes that act as molecular logic gates.

The human player has nine types of DNA strand, each with a sequence specific to a particular square. To make a move, one type of strand is added to all the squares, as all must be aware of the choice.


The DNA strands are the on-switch for the "deoxyribozyme" enzymes. The enzymes' output, when activated by the required DNA strand, is to snip apart molecules in the mixture, which produces the green glow.

The enzyme gates are carefully constructed and distributed so that after the human's move, the enzymes unlock only in one well. This is "quite ingenious" says Benenson. Because tic-tac-toe is a simple game, the computer could be designed so that it always wins or draws.

Stojanovic has lost to MAYA more than a 100 times. "We could have programmed it to lose sometimes, to make humans happy," he told New Scientist. "But to say 'the automaton can not be defeated' has a nice ring to it."

Journal reference: Nature Biotechnology (DOI:10.1038/nbt862)


Jenny Hogan

http://www.newscientist.com/news/news.jsp?id=ns99994063

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