Inside the cells, the man-made DNA got spliced into a plasmid, a circular piece of DNA found in bacteria. The plasmids replicated, without rejecting the foreign DNA or affecting the cells' growth, the researchers reported.
Now that the scientists have demonstrated an organism can incorporate artificial DNA letters into its genome, the next step will be showing it can convert the DNA into new proteins, which could be used to produce better drugs.
Proteins have become an important new type of drug, because cells can do the work of making them and because molecular biology techniques can be used to help proteins "evolve" to have desired properties, Romesberg said. But proteins are limited to only 20 building blocks, known as amino acids.
"Compare this to a medicinal chemist, who explores a much greater diversity of structures in the small-molecule drugs they synthesize," Romesberg said. "We hope to be able to combine the best of both small-molecule and protein drugs."
The research paves the way for "designer" organisms with custom-made genomes that are capable of performing useful tasks, like making drugs. Already, researchers have created the first "synthetic organisms" — artificial bacteria and yeast — which have man-made DNA sequences in their genomes.
The researchers are now working on expanding the DNA alphabet of yeast cells, and eventually hope to do the same for mammalian cells, which have properties that make them better at producing protein drugs.
Expanding the genetic alphabet of an entire multicellular organism such as a human wouldn't be possible with the current technique, however, because the artificial letters must be directly inserted into each cell, Romesberg said.
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