... YokogawaT, Okuni T, Nakayama H, Takio K, Yabuki T, KigawaT, Kodama K, Yokogawa T, Nishikawa K &Yokoyama S (2002) An unnatural base pair for incor-porating amino acid analogs into proteins. ... incorporation of unnatural amino acids, havetaken advantage of advances in cell- free translationsystems. The use of tRNA, mischarged with an un-natural amino acid through a chemical acylationmethod ... use of engineered aminoa-cyl-tRNA synthetases [38,39] and ribozymes [40] thatcan catalyze aminoacylation of tRNA with specificunnatural amino acids. In addition to amber codons,other target codons...