# Recently

By [Superme002](https://paragraph.com/@superme002) · 2021-10-28

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Recently, an additional rare amino acid pyrrolysine (Pyl), was identified, which expanded the canonical genetic code to 22 amino acids . Pyl is inserted in response to UAG codon in several methanogenic archaea . Although the mechanism of Pyl biosynthesis and incorporation into protein is not fully understood, the presence of a tRNApyl gene (_pylT_) with the CUA anticodon and of class II aminoacyl-tRNA synthetase gene (_pylS_) argued for cotranslational incorporation of Pyl . In _Desulfitobacterium hafniense_, a single bacterium, in which a Pyl-containing protein was found, PylS consists of two proteins: PylSn and PylSc .

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*Originally published on [Superme002](https://paragraph.com/@superme002/recently)*