DNA computer unbeaten at tic tac toe
Noughts and crosses automaton heralds medical robots.
21 August 2003
A DNA computer called MAYA has won every game of tic tac toe it has
played against human opponents - over 100 in all.
In the classic puzzle, also called noughts and crosses, two players
take turns to bag squares of a three-by-three grid, battling to complete the
first line. MAYA has a three-by-three array of wells in a plastic laboratory
dish, each filled with a unique*tail of enzymes1. Feeding it a
particular combination of DNA fragments triggers enzymes in one well to
generate a glowing dye.
A game begins when a human player adds magnesium to all of the wells.
This fires up the enzymes to play their first move - always the centre
Current rules dictate that the human then has to play either the top
left corner or left middle, by adding the appropriate DNA fragment to every
well - he or she has eight DNA pieces, each corresponding to the eight
remaining places on the board. The DNA causes enzymes in another of the
squares to glow, and so the game goes on.
MAYA never slips up - it is unbeatable even if its human opponent
plays perfectly, in which case there is a draw. It was invented by Milan
Stojanovic, of Columbia University in New York, and Darko Stefanovic, of the
University of New Mexico in Albuquerque.
A similar approach might be used to create other logic-puzzle
computers, says Stefanovic, such as one to solve the '*s and
missionaries' conundrum. Here players figure out how to ferry three
*s and three missionaries across a river, never allowing the hungry
to outnumber their prey.
Molecular automatons might one day find medical uses. Injected into
the *, they could recognize molecules on cancerous or healthy cells to
deliver a drug accurately. "We don't want to go too deep into games or the
[medical] community will not take us seriously," says Stojanovic.
a.. Stojanovic, M. N. & Stefanovic, D. A deoxyribozyme-based
molecular automaton. Nature Biotechnology, published online,
"Iran would be dangerous if they have a nuclear weapon."
- Washington, D.C., June 18, 2003
- President Bushisms
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