For billions of years, the history of life [on this planet] has been written with four letters — A, T, C and G, the labels given to the DNA subunits contained in all organisms. That alphabet has just grown longer, researchers announce, with the creation of a living cell that has two 'foreign' DNA building blocks in its genome.
“What we have now is a living cell that literally stores increased genetic information,” says Floyd Romesberg, a chemical biologist at the Scripps Research Institute in La Jolla, California, who led the 15-year effort.
Each strand of the DNA's double helix has a backbone of sugar molecules and, attached to it, chemical subunits known as bases. There are four different bases: adenine (A), thymine (T), cytosine (C) and guanine (G). These letters represent the code for the amino-acid building blocks that make up proteins. The bases bind the two DNA strands together, with an A always bonding to a T on the opposite strand (and vice versa), and C and G doing likewise.
Romesberg’s group is working on getting foreign DNA to encode proteins that contain amino acids other than the 20 that together make up nearly all natural proteins. Amino acids are encoded by 'codons' of three DNA letters apiece, so the addition of just two foreign DNA 'letters' would vastly expand a cell’s ability to encode new amino acids.
Potential uses of the technology include the incorporation of a toxic amino acid into a protein to ensure that it kills only cancer cells, and the development of glowing amino acids that could help scientists to track biological reactions under the microscope.
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