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Biological transistor built for living computers

DNA-based switches could be used in diagnosis and treatment of diseases

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Save the clunky tricorders for Star Trek. One day, tiny biological computers with DNA-based circuitry could diagnose diseases.

Using snippets of DNA and DNA-clipping chemicals, researchers have created one key component of a computer’s brain: the transistor, a switch that helps electronics perform logic. The biological switch, dubbed a transcriptor, could be plugged together with other biological devices to boost the power of DNA-based computers, researchers report March 28 in Science.

With these switches, researchers might be able to program probiotic bacteria — the kind found in yogurt — to detect signs of colon cancer and then spit out warning signals, says study coauthor Jerome Bonnet of Stanford University. “The bacteria could actually travel through your gut and make a color in your poop,” he says.

Inside every smartphone, television and iPod, a computer chip holds circuits loaded with millions of transistors. By flipping on or off, the tiny switches direct electrical current to different parts of the chip. But inside cells, even just a few linked-up switches could be powerful, says synthetic biologist Timothy Lu of MIT. The simple circuits “probably wouldn’t be able to compute square roots,” he says, “but you don’t need to put a MacBook chip inside a cell to get some really interesting functions.” And genetic computers can go places conventional electronics can’t.

Instead of controlling the flow of electrons across metal circuit wires, the biological switches control the flow of a protein along a “wire” of DNA in living bacteria. As the protein chugs along the wire, it sends out messages telling the cell to make specific molecules — molecules that color a person’s poop green, for example.

Bonnet toggled the switch on and off with wire-clipping enzymes that can snip out a section of DNA and flip it backward. Like cars driving over the one-way spike strip out of an airport parking lot, the message-making protein moved forward only when DNA faced the right direction.

By linking together different switches and wire clippers, the researchers were able to program a cell’s behavior. They could make bacteria glow green only when sugar was around, for example, or only when sugar and a drug were nearby.

Even this simple logic — responding to just one or two inputs with different actions — is useful, Bonnet says, because it lets researchers program cells to react to specific chemical cues.

Though genetic computers aren’t going to replace your laptop, he says, his group and others are trying to make the tiny devices even more efficient. In past research, the team has created DNA-based data storage (SN: 6/30/12, p. 14) and figured out how to send genetic information between cells. Now, bioengineers are working on scaling up biological devices by plugging together different components and linking individual computers to form a multicellular “Internet.”

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