Archaea Decode UAG as Dual Roles, Expanding the Genetic Code

UC Berkeley researchers report that the methane-producing archaeon Methanosarcina acetivorans can interpret the UAG stop codon as either a termination signal or as the amino acid pyrrolysine, producing two protein forms from the same gene. The availability of pyrrolysine appears to influence the outcome, and about 200–300 genes may be affected, suggesting that genetic decoding can be context-dependent. This challenges the view of a single fixed genetic code and could inform new strategies for treating diseases caused by premature stop codons and expanding microbial biochemistry.