A computer in every cell

Scientists have designed a “biological computer” that can calculate logical expressions using RNA implanted in living cells.

The advance could eventually lead to new tools for biologists studying the inner workings of cells. It could also lead to “smart medicines” that respond in preprogrammed ways to a patient’s state of health. “It’s a great way to do . . . logic,” says Yaakov Benenson of Harvard University. Our system “can basically make decisions based on multiple [input] signals,” he adds.

The computer consists of several kinds of engineered RNA molecules produced by synthetic DNA that Benenson’s team inserted into cultured human-kidney cells. Each input for the computer would be either the presence (a logical “true”) or absence (“false”) in the cell of some molecule, perhaps a cancer-related protein. To make the connections between inputs and outputs, the scientists constructed logical circuits with a type of RNA called small interfering RNA (siRNA), which can control the activity of other RNAs. The team assembled these units into a network of biological switches that produces an output by triggering a gene to become active or not active.

That gene might produce a fluorescent protein to signal to a doctor when disease is present or make an enzyme that either repairs or kills a precancerous cell.

The system that Benenson’s team designed had five inputs, but it could be scaled up to compute any logical expression with many inputs and outputs, the team reports in the July Nature Biotechnology.