The dawn of biological computers is at hand. In a major first for synthetic biology, Stanford engineers have used genetic material to create a biological transistor. Called the "transcriptor," the creation is the final, missing component necessary for the creation of a biological computer that could enable researchers to program functions into living cells.
Modern computers rely on three standard functions. One: they must be able to store information. Two: they have to be able to transmit information. Three: they need a basic system of logic – a set of rules that governs how they should function given one or more forms of input. A biological computer would implement all three on a cellular level, using proteins and DNA in place of silicon chips.
The first two functions have been demonstrated with cellular materials before. Several labs have now demonstrated the ability to store digital data in DNA, some of them at jaw-dropping densities; and last year, a team led by Stanford bioengineer Drew Endy developed a system for transmitting genetic information between cells. Now, in a study recounted in the latest issue of Science, Endy's team has developed what it calls a "transcriptor" – the biological equivalent of a digital transistor – and with it a system of logic that can control cellular function.
In your standard computer, transistors govern the flow of electricity by playing red light/green light with electrons along a circuit. Similarly, a transcriptor regulates the flow of a protein called RNA polymerase along a strand of DNA. Transistors and transcriptors are, at their most basic, on/off switches – the gatekeepers of information transmission, storage, amplification, and so forth.
The rules that these gatekeepers follow give rise to the logic systems that dictate what problems a computer can solve. A transcriptor gatekeeper that lives by a code of "AND," for example, might allow RNA polymerase to continue along a strand of DNA when two predetermined conditions are "true" – if, for example, the transcriptor detects the presence of Enzyme-A AND Enzyme-B inside the cell.
A transcriptor that abides by the code of "OR," on the other hand, would allow RNA polymerase to continue when either or both of the enzymes are present. In computer science, transistors that abide by AND-/NAND-/OR-/XOR-/NOR-/XNOR-rules (which you can read all about here) are called Boolean logic gates. Endy calls his transcriptor equivalents Boolean Integrase Logic gates. Or "BIL" gates, for short. Below, Endy provides an in-depth explanation of Transcriptors and BIL gates.
Here's the takeaway: if you line a bunch of these logic gates up, you form a logic circuit. Get enough logic circuits together, and you have a computer that can handle just about any computation you throw at it – whether it's addition and subtraction on a calculator, or gene expression inside a cell.
Endy plans on starting small. For now, he's working with bacteria, helping other researchers use his BIL gates to engineer E. coli that can be programmed to change color. And in a refreshingly practical take on the potential applications of his team's creation, Endy told NPR's Morning Edition that he doubts these DNA computers will ever outwit your iPhone; but this, he said, is missing the point.
"We're building computers that will operate in a place where your cellphone isn't going to work."
Endy's team's research is published in the latest issue of Science. For a fantastic animated explanation of Transcriptors, check out this series of graphics created by Adam Cole for NPR.
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