What if tRNAs can code for 34 amino acids?

The role of tRNAs in protein production. Credit: National Human Genome Research Institute with edits by the HMS Office of Communications and External Relations

For billions of years, life has built proteins using the same molecular alphabet: just 20 amino acids. Now, scientists have found a way to expand that alphabet dramatically.

Researchers at Harvard Medical School and the Wyss Institute have developed AGENTEX, a system that can create proteins using up to 34 amino acids, without rewriting the DNA of a living organism.

AGENTEX enables multiplexed testing of genetic codes and sequence-defined biopolymer synthesis. Credit: Nature (2026). DOI: 10.1038/s41586-026-10949-y

That distinction matters. Previous attempts to expand the genetic code required painstakingly modifying organisms such as E. coli. The process could take years for each additional amino acid and sometimes disrupted normal cellular functions.

AGENTEX takes a different route. Instead of altering living cells, researchers work in cell free mixtures containing the molecular machinery required for protein production. Engineered transfer RNAs and ribosomes can be programmed to recognize customized genetic codes and incorporate new building blocks into proteins.

The researchers also uncovered a surprising biological detail. Scientists had long believed that functional tRNAs essentially required a CCA sequence at their ends. AGENTEX revealed that some alternative sequences, including CGA, can still support amino acid attachment.

The result is more than a new protein engineering tool. It offers scientists a programmable molecular system for exploring entirely new proteins and potentially creating future medicines, biomaterials, food technologies and environmental solutions.