But because biology is so flexible, that genetic code is sometimes tweaked to add additional amino acids into select proteins. It turns out that some archaea, microorganisms distinct from bacteria and eukaryotes, have gone one step further. A research team led by Veronika Kivenson and Jill Banfield<\/a> at the University of California, Berkeley, has found multiple lineages of archaea that have fully repurposed the TAG stop codon to encode the noncanonical amino acid pyrrolysine<\/a> (Science 2025, DOI: 10.1126\/science.adu2404). That repurposing has created a distinct genetic code with 62 sense codons encoding 21 amino acids, the researchers say.<\/p>\n Pyrrolysine is an important component of methyltransferase enzymes, which the archaea use to metabolize methylamine in the environment. \u201cThe need for that metabolism and availability of the machinery to use pyrrolysine apparently drove the broad adoption of the new code,\u201d Kivenson and Banfield say via email.<\/p>\n The pair say that \u201cthe specific pattern of *which* archaea have an alternative genetic code points to the fact that this alternative genetic code has arisen multiple times – this means that the genetic code – the really fundamental core of biology – has more tolerance to change than previously thought.\u201d<\/p>\n Beyond evolutionary implications, the work also has synthetic biologists excited. Jeffery M. Tharp<\/a>, a chemical and synthetic biologist at Indiana University who studies noncanonical amino acids and genetic code expansion, says that pyrrolysine transfer RNA (tRNA) synthetase from these archaea could also be used to install other unnatural amino acids into proteins. \u201cAnd the idea is that that will allow us to produce new materials with completely unprecedented properties.\u201d<\/p>\n Tharp also says that dream is still a long way off but that the new work is \u201can exciting step towards that.\u201d<\/p>\n
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