Bioengineers at Stanford University have created the first biological transistor made from genetic materials: DNA and RNA. Dubbed the “transcriptor,” this biological transistor is the final component required to build biological computers that operate inside living cells. We are now tantalizingly close to biological computers that can detect changes in a cell’s environment, store a record of that change in memory made of DNA, and then trigger some kind of response — say, commanding a cell to stop producing insulin, or to self-destruct if cancer is detected.

Stanford’s transcriptor is essentially the biological analog of the digital transistor. Where transistors control the flow of electricity, transcriptors control the flow of RNA polymerase as it travels along a strand of DNA. The transcriptors do this by using special combinations of enzymes (integrases) that control the RNA’s movement along the strand of DNA. “The choice of enzymes is important,” says Jerome Bonnet, who worked on the project. “We have been careful to select enzymes that function in bacteria, fungi, plants and animals, so that bio-computers can be engineered within a variety of organisms.”

Like a transistor, which enables a small current to turn on a larger one, one of the key functions of transcriptors is signal amplification. A tiny change in the enzyme’s activity (the transcriptor’s gate) can cause a very large change in the two connected genes (the channel). By combining multiple transcriptors, the Stanford researchers have created a full suite of Boolean Integrase Logic (BIL) gates — the biological equivalent of AND, NAND, OR, XOR, NOR, and XNOR logic gates. With these BIL gates (pun possibly intended), a biological computer could perform almost computation inside a living cell.

You need more than just BIL gates to make a computer, though. You also need somewhere to store data (memory, RAM), and some way to connect all of the transcriptors and memory together (a bus). Fortunately, as we’ve covered a few times before, numerous research groups have successfully stored data in DNA — and Stanford has already developed an ingenious method of using the M13 virus to transmit strands of DNA between cells. (See: Harvard cracks DNA storage, crams 700 terabytes of data into a single gram.) In short, all of the building blocks of a biological computer are now in place.

This isn’t to say that highly functional biological computers will arrive in short order, but we should certainly begin to see simple biological sensors that measure and record changes in a cell’s environment. Stanford has contributed the BIL gate design to the public domain, which should allow other research institutes, such as Harvard’s Wyss Institute, to also begin work on the first biological computer. (See: The quest for the $1000 genome.)

Moving forward, though, the potential for real biological computers is immense. We are essentially talking about fully-functional computers that can sense their surroundings, and then manipulate their host cells into doing just about anything. Biological computers might be used as an early-warning system for disease, or simply as a diagnostic tool (has the patient consumed excess amounts of sugar, even after the doctor told them not to?) Biological computers could tell their host cells to stop producing insulin, to pump out more adrenaline, to reproduce some healthy cells to combat disease, or to stop reproducing if cancer is detected. Biological computers will probably obviate the use of many pharmaceutical drugs.

Now read: IBM takes a step towards building artificial semiconductor synapses

Research paper: DOI: 10.1126/science.1232758 – “Amplifying Genetic Logic Gates”