A DNA double helix built from eight hachimoji building blocks: G (green), A (red), C (dark blue), T (yellow), B (cyan), S (pink), P (purple) and Z (orange). The first four building blocks are found in human DNA; the last four are synthetic. Each strand of the double helix has the sequence CTTAPCBTASGZTAAG. Image credit: Millie Georgiadis/ Indiana University School of Medicine.
A team of synthetic biologists led by Steven Benner at the Foundation for Applied Molecular Evolution—and including Andrew Ellington at The University of Texas at Austin—have synthesized a new kind of DNA that uses eight building blocks instead of the four found in all earthly life. Reporting today in the journal Science, the researchers suggest the new eight-letter DNA could find applications in medicine and biological computing. The finding also has implications for how scientists think about life elsewhere in the universe.
"Four-letter DNA was given to us by evolution," said Ellington. "The fact that we can now, as humans, go beyond nature, that is huge."
The new DNA doubles the four building blocks found in natural DNA, making a new 8-letter synthetic genetic system called "hachimoji" DNA (from Japanese "hachi" meaning "eight," and "moji" meaning "letter," as in "emoji").
One possible application might be in a new biological information storage system that would store data at much higher densities than current silicon-based systems.
Benner's company, Firebird Biomolecular Sciences, is working to commercialize hachimoji for medical applications including disease diagnosis and the development of new drugs.
Ellington's team at UT Austin found a mutant enzyme that could better copy hachimoji DNA into hachimoji RNA. The transfer of this level of information from one biopolymer to another is unprecedented in the field of synthetic biology. This is analogous to the way that earthly life "transcribes" DNA into RNA as part of the process of making proteins from the information stored in DNA. Next, Ellington's team plans to develop an enzyme for replicating strands of hachimoji DNA, what is known as a DNA polymerase.
The research also has implications for understanding life elsewhere in the universe. Eight-letter DNA shares many of the same characteristics that make ordinary four-letter DNA suitable for storing a genetic code for life. For example, each possible pair of letters has the same shape and size as every other pair, making them interchangeable. If a single letter in the code can be easily swapped out with another—in other words, if genes can easily mutate—then a species can evolve over time, a hallmark of life. The researchers suggest that traits like this mean such an expanded form of DNA could form the basis of life on other planets.
This work was supported by NASA and the Templeton World Charity Foundation, the Department of Energy, the National Science Foundation, and the National Institutes of Health.
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