biology · global
The Same Set of Genetic Code Can Somehow Say Two Things in Archaeal Cells
A UC Berkeley team has found in methane-producing archaea that the UAG codon, which usually means “stop,” is sometimes reread as a rare amino acid, opening a measurable gap in one of life’s most stable translation rules.
The genetic code is often described as life’s shared language: three letters in DNA correspond to one amino acid, or tell the cell when to stop making a protein. This set of rules matters not only because it underpins the molecular biology found in every textbook, but also because modern genetic engineering, disease diagnosis, and protein design almost all assume that cells will read each codon in a stable and unambiguous way.
UC Berkeley researchers have now found an exception in a methane-producing archaeon, Methanosarcina acetivorans. According to research summarized by ScienceDaily and Berkeley News, this archaeon can read the UAG codon as two signals: sometimes it is the classic stop sign, causing protein synthesis to halt; at other times it is read as the rare amino acid pyrrolysine, allowing the ribosome to keep translating.
This is not simply a “misreading.” The study indicates that the same gene sequence may therefore produce protein products of different lengths and different compositions, as if tossing a coin at the molecular level. Berkeley News said the related PNAS paper was published on November 6, 2025, with UC Berkeley’s Dipti Nayak as senior author and Katie Shalvarjian as first author; the report also noted that about 200 to 300 genes in the M. acetivorans genome contain UAG, meaning this dual reading may not be an isolated phenomenon.
The key may lie in the supply of pyrrolysine inside the cell. If this rare amino acid and the corresponding translation machinery are relatively abundant, UAG is more likely to be treated as “continue”; if conditions are insufficient, it returns to the role of a stop signal. In other words, environmental and metabolic states may affect which protein the same stretch of genetic information ultimately becomes, adding to gene expression a layer of regulation that is more fluid than the sequence itself.
This finding challenges a long-standing and highly practical assumption: within the same organism, the meaning of each codon is largely fixed. Popular Mechanics’ science coverage also connected this point to broader biomedical possibilities, including whether similar mechanisms might one day offer lessons for addressing genetic diseases caused by premature stop codons, such as cystic fibrosis or Duchenne muscular dystrophy. However, this remains a conceptual inspiration; the current research subject is archaea, not human cells, and it is not a clinical treatment strategy.
More cautiously, this study reveals the flexibility of life’s translation system, but it has not yet answered how much adaptive advantage it provides in natural environments, which proteins are most affected, or whether this “dual meaning” can be reliably engineered. What is truly intriguing may not be that it overturns the genetic code, but that it reminds us: even life’s most fundamental grammar may, in the survival strategies of a few organisms, preserve finer shades of gray than humans have imagined.