bio game

[A!]

*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