Editing Transfer RNA (section)

=== Engineered tRNAs ===
{{main|Genetic code expansion}}
tRNAs with modified anticodons and/or acceptor stems can be used to modify the genetic code. Scientists have successfully repurposed codons (sense and stop) to accept amino acids (natural and novel), for both initiation (see: [[start codon]]) and elongation.

In 1990, tRNA{{sup sub|fMet2|CUA}} (modified from the tRNA{{sup sub|fMet2|CAU}} gene [https://ecocyc.org/gene?orgid=ECOLI&id=EG30061 metY]) was inserted into ''E. coli'', causing it to initiate protein synthesis at the UAG stop codon, as long as it is preceded by a strong [[Shine-Dalgarno sequence]]. At initiation it not only inserts the traditional [[formylmethionine]], but also formylglutamine, as glutamyl-tRNA synthase also recognizes the new tRNA.<ref>{{cite journal |last1=Varshney |first1=U |last2=RajBhandary |first2=U L |title=Initiation of protein synthesis from a termination codon. |journal=Proceedings of the National Academy of Sciences |date=February 1990 |volume=87 |issue=4 |pages=1586–1590 |doi=10.1073/pnas.87.4.1586|doi-access=free |pmid=2406724 |pmc=53520 |bibcode=1990PNAS...87.1586V }}</ref> The experiment was repeated in 1993, now with an elongator tRNA modified to be recognized by the [[methionyl-tRNA formyltransferase]].<ref>{{cite journal |last1=Varshney |first1=U |last2=Lee |first2=C P |last3=RajBhandary |first3=U L |title=From elongator tRNA to initiator tRNA. |journal=Proceedings of the National Academy of Sciences |date=15 March 1993 |volume=90 |issue=6 |pages=2305–2309 |doi=10.1073/pnas.90.6.2305|doi-access=free |pmid=8460138 |pmc=46075 |bibcode=1993PNAS...90.2305V }}</ref> A similar result was obtained in ''[[Mycobacterium]]''.<ref>{{cite journal | vauthors = Govindan A, Miryala S, Mondal S, Varshney U | title = Development of Assay Systems for Amber Codon Decoding at the Steps of Initiation and Elongation in Mycobacteria | journal = Journal of Bacteriology | volume = 200 | issue = 22 | date = November 2018 | pmid = 30181124 | pmc = 6199473 | doi = 10.1128/jb.00372-18 }}</ref> Later experiments showed that the new tRNA was orthogonal to the regular AUG start codon showing no detectable off-target translation initiation events in a genomically recoded ''E. coli'' strain.<ref name="fmet2-cua-ec">{{cite journal | vauthors = Vincent RM, Wright BW, Jaschke PR | title = Measuring Amber Initiator tRNA Orthogonality in a Genomically Recoded Organism | journal = ACS Synthetic Biology | volume = 8 | issue = 4 | pages = 675–685 | date = April 2019 | pmid = 30856316 | doi = 10.1021/acssynbio.9b00021 | s2cid = 75136654 }}</ref>