Inside every cell is a chef of sorts, cooking up the “cuisine” that makes life possible—a vast array of proteins. Now scientists have built an alien chef, capable of cooking from recipes written in artificial DNA to make novel proteins that might serve as antibiotics, biofuels or other useful molecules.

In the typical order of things, these chefs, known as ribosomes, are made of two pieces of RNA and amino acids that work together briefly to build proteins and then go their own ways when the job is done. Biological engineer Michael Jewett of Northwestern University and pharmaceutical biotechnologist Alexander Mankin of the University of Illinois at Chicago decided to try something new: tethering the two parts of their synthetic ribosome, Ribo-T, to each other so it could continue to follow the same set of novel instructions. No prior life on earth—either evolved in the wild or made by scientists in the laboratory—is known to have ever had or lived with such a tied-up ribosome.

This new chef cooks just fine, however. Ribo-T successfully built green, fluorescing proteins. And Escherichia coli with only the synthetic ribosomes lived nearly as well as wild peers. Further, the E. coli passed Ribo-T on to its offspring. “This alien will help us better understand how normal ribosomes work,” Mankin says.

In fact, this study reveals something heretofore unknown: ribosomes do not have to be promiscuous to work—the two units that usually combine and separate can be tethered together permanently without killing the cell. Plus, the alien ribosome and a more typical one can work side by side, one cooking up the unique proteins while the other churns out the enzymes necessary to keep the cell alive. DARPA supported the work as part of the agency's effort to craft living foundries for new materials, whether medicinal molecules or better biofuels.

Base pairs that exist only in the lab, rearranged chromosomes, even entire synthetic genomes—all have been made by scientists in recent years. Now add to the synthetic biologist's toolbox a new ribosome, a designer chef that can cook up new dishes with de novo ingredients such as “unnatural” amino acids. Bon appétit.