Editing Stop codon (section)

=== Translation ===
In 1986, convincing evidence was provided that [[selenocysteine]] (Sec) was incorporated co-translationally. Moreover, the codon partially directing its incorporation in the polypeptide chain was identified as UGA also known as the opal termination codon.<ref>{{cite journal |pages=4650–4 |doi=10.1073/pnas.83.13.4650 |title=Nucleotide sequence and expression of the selenocysteine-containing polypeptide of formate dehydrogenase (formate-hydrogen-lyase-linked) from Escherichia coli |year=1986 |last1=Zinoni |first1=F |last2=Birkmann |first2=A |last3=Stadtman |first3=T |last4=Böck |first4=A |journal=Proceedings of the National Academy of Sciences |volume=83 |issue=13 |pmid= 2941757|pmc=323799 |bibcode=1986PNAS...83.4650Z |doi-access=free }}</ref> Different mechanisms for overriding the termination function of this codon have been identified in prokaryotes and in eukaryotes.<ref>{{cite book |last1=Böck |first1=A |title=Encyclopedia of Biological Chemistry |chapter=Selenoprotein Synthesis |year=2013 |pages=210–3 |doi=10.1016/B978-0-12-378630-2.00025-6 |isbn=978-0-12-378631-9 |chapter-url=https://www.sciencedirect.com/science/article/pii/B9780123786302000256 |access-date=23 August 2021}}</ref> A particular difference between these kingdoms is that cis elements seem restricted to the neighborhood of the UAG codon in prokaryotes while in eukaryotes this restriction is not present. Instead such locations seem disfavored albeit not prohibited.<ref>{{cite journal |last1=Mix |first1=H |last2=Lobanov |first2=A |last3=Gladyshev |first3=V |title=SECIS elements in the coding regions of selenoprotein transcripts are functional in higher eukaryotes |journal=Nucleic Acids Research |date=2007 |volume=35 |issue=2 |pages=414–423 |doi=10.1093/nar/gkl1060 |pmid=17169995 |url=https://academic.oup.com/nar/article/35/2/414/2400734|pmc=1802603 }}</ref>

In 2003, a landmark paper described the identification of all known selenoproteins in humans: 25 in total.<ref>{{cite journal |last1=Kryukov |first1=G |last2=Gladyshev |first2=V |title=Characterization of mammalian selenoproteomes |journal=Science |date=2003 |volume=300 |issue=5624 |pages=1439–43 |doi=10.1126/science.1083516 |pmid=12775843 |bibcode=2003Sci...300.1439K |s2cid=10363908 |url=https://www.science.org/doi/full/10.1126/science.1083516}}</ref> Similar analyses have been run for other organisms.

The UAG codon can translate into [[pyrrolysine]] (Pyl) in a similar manner.