Two chemists at the California Institute of Technology have engineered a cellular "computer" within the genetic material of living yeast cells. The cells can signal the presence or absence of two drugs in their environment — theophylline, a former asthma treatment, and tetracycline, an antibiotic — by activating a gene that makes a fluorescent protein.

The cell engineers, Maung Nyan Win and Christina D. Smolke, have programmed several simple logical operations. A cell can signal when both drugs are present (AND, in the parlance of computer programmers), when either one or the other is present (OR), when neither is present (NOR), or when either one drug or neither of them is present (NAND).  

To build their biocomputer, Win and Smolke inserted three kinds of RNA into yeast cells: aptamers, which bind to specific molecules; enzymes called ribozymes; and "transmitter" sequences that let the aptamers turn the ribozymes on or off. They deployed a small set of aptamers, ribozymes, and transmitters, in various combinations, to program the logical operations. The foreign RNA worked independently of the cells' own machinery without hampering its normal function.

Win and Smolke's feat is a step toward the development of programmable cellular tools that could one day help detect cancer, selectively deliver drugs to sick organs, degrade specific pollutants, enhance food production, and more.

The findings were reported in the journal Science.

Editor's Note: This article was updated March 31, 2009 to accurately describe the logic operations involved.