title: Is there a twenty third amino acid in the genetic code?
abstract: The universal genetic code includes 20 common amino acids. In addition, selenocysteine (Sec) and pyrrolysine (Pyl), known as the twenty first and twenty second amino acids, are encoded by UGA and UAG, respectively, which are the codons that usually function as stop signals. The discovery of Sec and Pyl suggested that the genetic code could be further expanded by reprogramming stop codons. To search for the putative twenty third amino acid, we employed various tRNA identification programs that scanned 16 archaeal and 130 bacterial genomes for tRNAs with anticodons corresponding to the three stop signals. Our data suggest that the occurrence of additional amino acids that are widely distributed and genetically encoded is unlikely.
authors.affiliation: Department of Biochemistry, University of Nebraska, Lincoln, NE 68588, USA.
authors.forename: Alexey V
authors.initials: AV
authors.lastname: Lobanov
authors.forename: Gregory V
authors.initials: GV
authors.lastname: Kryukov
authors.forename: Dolph L
authors.initials: DL
authors.lastname: Hatfield
authors.forename: Vadim N
authors.initials: VN
authors.lastname: Gladyshev
mesh_terms: D000596:Amino Acids / Q000235:genetics*; D018388:Codon, Terminator; D019295:Computational Biology; D005815:Genetic Code; D020745:Genome, Archaeal; D016680:Genome, Bacterial; D008239:Lysine / Q000031:analogs & derivatives / Q000235:genetics; D009690:Nucleic Acid Conformation; D012343:RNA, Transfer / Q000235:genetics*; D017279:Selenocysteine / Q000235:genetics
chemical_list: D000596:Amino Acids; D018388:Codon, Terminator; D017279:Selenocysteine; D012343:RNA, Transfer; C456839:pyrrolysine; D008239:Lysine