Life on Earth has always used four DNA letters, but scientists have created a bigger genetic alphabet and found something unexpected

For billions of years, life on Earth has relied on a remarkably simple genetic language.

DNA uses just four chemical letters — A, T, C and G — to store the instructions needed to build and maintain living organisms. Every known form of life uses this same basic genetic alphabet.

Now, scientists have taken an important step toward rewriting that rule.


Researchers at the University of California San Diego have shown that RNA polymerase, a key enzyme responsible for reading genetic information, can accurately recognise and transcribe DNA containing eight genetic letters instead of four.

The finding does not mean scientists have created an eight-letter living organism. But it demonstrates something potentially important: some of the molecular machinery already found inside cells may be capable of processing genetic information that nature itself never evolved.

That could open new possibilities for synthetic biology, where researchers attempt to build biological systems with functions beyond those found in nature.

DNA may not be limited to four letters

The genetic alphabet used by natural life consists of four bases: adenine, thymine, cytosine and guanine.

These bases pair up in specific combinations to form the familiar structure of DNA.

Scientists have spent years asking whether that four-letter system represents a fundamental limit of biology or simply the alphabet that evolution happened to settle on.

One approach has been to create unnatural base pairs, synthetic chemical building blocks that can be incorporated into DNA alongside the four natural bases.

Together, these can create an expanded genetic alphabet.

One of the most ambitious examples is known as Hachimoji DNA, a system based on eight genetic letters. The name comes from Japanese words meaning “eight” and “letter”.

The latest research addresses a crucial question: even if scientists can build DNA containing these artificial letters, can the molecular machinery inside a cell actually read the information?

Researchers watched an enzyme read synthetic DNA

The team focused on RNA polymerase, an enzyme that plays a central role in gene expression.

When a cell needs to use information stored in a gene, RNA polymerase moves along the DNA and produces an RNA copy. That RNA can then be used in subsequent steps of cellular activity.

For synthetic DNA to become genuinely useful, researchers need more than the ability to manufacture it.

The genetic information has to be read accurately and converted into RNA.

To investigate this process, the scientists combined biochemical experiments with high-resolution structural imaging.

They examined RNA polymerase from Escherichia coli, commonly known as E. coli, as it interacted with two synthetic base pairs incorporated into DNA.

The researchers used cryo-electron microscopy to capture detailed snapshots of the molecular machinery at work.

The enzyme appears to recognise more than scientists expected

The structural images offered a glimpse into how RNA polymerase handles artificial genetic letters.

Rather than treating the synthetic bases as completely foreign objects, the enzyme appeared to use several of the same structural and chemical signals involved in recognising ordinary DNA base pairs.

That helps explain how RNA polymerase can distinguish the artificial genetic information and incorporate the corresponding RNA building blocks with a high degree of accuracy.

The discovery is important because transcription is one of the major hurdles in creating an expanded genetic system.

It is one thing to design an artificial DNA molecule.

It is another to persuade the molecular machinery of a living cell to read that DNA as meaningful biological information.

A second experiment produced an even stranger result

The UC San Diego researchers have also been investigating another type of synthetic base pair.

In a separate study published in Proceedings of the National Academy of Sciences in August, the team reported that RNA polymerase could recognise and process a synthetic base pair even though the bases do not rely on the conventional hydrogen bonds normally associated with DNA base pairing.

Instead, the artificial pair can remain associated through different chemical interactions.

That result challenges the assumption that the hydrogen-bonding patterns found in natural DNA are absolutely necessary for cellular transcription.

Together, the two studies provide researchers with a clearer picture of how flexible the molecular machinery of life may actually be.

Why eight-letter DNA could matter

The significance of expanded DNA is not simply that scientists can add four more letters to a genetic sequence.

A larger alphabet dramatically increases the number of possible sequences that can be constructed.

With four letters, biology has an enormous number of possible DNA sequences to work with. Adding additional chemical building blocks expands that design space even further.

That could allow scientists to create genetic molecules with properties that are difficult or impossible to achieve using natural DNA alone.

Researchers are particularly interested in using expanded genetic systems to develop molecules that can recognise specific biological targets, create new types of chemical reactions or produce compounds that ordinary biology cannot make.

Synthetic DNA has already shown medical potential

The idea is not purely theoretical.

Earlier research has explored expanded genetic alphabets for applications such as synthetic DNA molecules designed to recognise cancer cells.

Such technologies could eventually contribute to new approaches in diagnostics or targeted therapies, although substantial research would be required before laboratory concepts could become practical medical treatments.

The ability to transcribe artificial genetic information could make these systems considerably more powerful.

If synthetic DNA can reliably be converted into RNA inside a biological system, scientists could potentially use expanded genetic information to instruct cells to make molecules with unusual properties.

That is where the research begins to move from an interesting molecular experiment toward a broader synthetic biology platform.

Scientists are testing the boundaries of life's genetic machinery

The deeper question behind the research is surprisingly fundamental.

How much of the genetic machinery used by life is tied specifically to Earth's four-letter genetic code — and how much of it is flexible enough to work with entirely different chemical building blocks?

The new findings suggest that at least some of the machinery is more adaptable than previously assumed.

RNA polymerase evolved to work with natural genetic material, yet it can interact with carefully designed synthetic bases and still carry out the essential process of transcription.

That flexibility could prove valuable for researchers attempting to construct biological systems that operate outside the constraints of natural evolution.

An eight-letter genetic code could expand the biological toolbox

The research led by Dong Wang, a professor at UC San Diego's Skaggs School of Pharmacy and Pharmaceutical Sciences, represents part of a broader effort to understand and engineer expanded genetic systems.

The Nature Communications study, titled “Structural Basis of Transcription of the Hachimoji Eight-Letter Alphabet by E. coli RNA Polymerase,” was published on September 2, 2026.

The related PNAS research appeared on August 12, 2026.

Neither study shows that life naturally uses an eight-letter genetic code, nor do they demonstrate that an organism with such a genome can function normally from beginning to end.

What they do show is that a central component of the cellular machinery can handle genetic information that does not exist in natural biology.

That distinction is important — but so is what it could eventually make possible.

For decades, DNA has been viewed as life's universal information-storage system, built around four letters that appear almost impossibly fundamental.

Scientists are now discovering that the machinery reading those instructions may not be quite as constrained as the genetic alphabet itself.

And if researchers can eventually make expanded DNA, RNA and proteins work together reliably inside living cells, the four-letter genetic code may no longer be the only biological language scientists can engineer.