A microbe was discovered that used the codon UAG as a stop codon and as a code for the amino acid pyrrolysine. Pyrrolysine, found in archaea and bacteria, is required for methylamine-mediated methanogenesis, a form of anaerobic respiration. Typically, ambiguity in the code of DNA is deleterious, but with this microbe, it has created a new feature. This microbe has broken one of the fundamental rules of genetics, and biology as a whole, that each codon only has one meaning. The way that it is decided whether UAG will create the amino acid or to use it as a stop codon is seemingly random. The biggest connection that was found is that when less of the amino acid was around the cell, UAG more often acted as a stop codon. This study has created many questions around ways cells interpret stop codons, and if scientists have the ability to control them.
Sources:
https://www.pnas.org/doi/10.1073/pnas.2517473122
https://www.aol.com/lifestyle/scientists-discovered-creature-breaks-fundamental-130000934.html
I think this post is very interesting because it challenges one of the most fundamental principles of genetics that we've learned. UAG is supposed to code for termination of amino acid sequence, but this microbe can use the sequence to code for a specific amino acid as well as a stop signal.
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