Simplification of the genetic code: restricted diversity of genetically encoded amino acids.
At earlier stages in the evolution of the universal genetic code, fewer than 20 amino acids were considered to be used. Although this notion is supported by a wide range of data, the actual existence and function of the genetic codes with a limited set of canonical amino acids have not been addressed experimentally, in contrast to the successful development of the expanded codes. Here, we constructed artificial genetic codes involving a reduced alphabet. In one of the codes, a tRNAAla variant with the Trp anticodon reassigns alanine to an unassigned UGG codon in the Escherichia coli S30 cell-free translation system lacking tryptophan. We confirmed that the efficiency and accuracy of protein synthesis by this Trp-lacking code were comparable to those by the universal genetic code, by an amino acid composition analysis, green fluorescent protein fluorescence measurements and the crystal structure determination. We also showed that another code, in which UGU/UGC codons are assigned to Ser, synthesizes an active enzyme. This method will provide not only new insights into primordial genetic codes, but also an essential protein engineering tool for the assessment of the early stages of protein evolution and for the improvement of pharmaceuticals.
Department of Computational Intelligence and Systems Science, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Midori-ku, Yokohama-shi, Kanagawa 226-8503, Japan.
Akio
A
Kawahara-Kobayashi
Akiko
A
Masuda
Yuhei
Y
Araiso
Yoko
Y
Sakai
Atsushi
A
Kohda
Masahiko
M
Uchiyama
Shun
S
Asami
Takayoshi
T
Matsuda
Ryuichiro
R
Ishitani
Naoshi
N
Dohmae
Shigeyuki
S
Yokoyama
Takanori
T
Kigawa
Osamu
O
Nureki
Daisuke
D
Kiga
D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D003062:Codon; D005815:Genetic Code; D014644:Genetic Variation; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D015202:Protein Engineering; D012344:RNA, Transfer, Ala / Q000737:chemistry; D012697:Serine Endopeptidases / Q000096:biosynthesis / Q000235:genetics; D000099160:LexA Repressor Protein
D001426:Bacterial Proteins; D003062:Codon; D012344:RNA, Transfer, Ala; D012697:Serine Endopeptidases; D000099160:LexA Repressor Protein