Enlarging the Amino Acid Set of Escherichia coli by Infiltration of the Valine Coding Pathway

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Science  20 Apr 2001:
Vol. 292, Issue 5516, pp. 501-504
DOI: 10.1126/science.1057718

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Aminoacyl transfer RNA (tRNA) synthetases establish the rules of the genetic code by catalyzing the aminoacylation of tRNAs. For some synthetases, accuracy depends critically on an editing function at a site distinct from the aminoacylation site. Mutants ofEscherichia coli that incorrectly charge tRNAValwith cysteine were selected after random mutagenesis of the whole chromosome. All mutations obtained were located in the editing site of valyl-tRNA synthetase. More than 20% of the valine in cellular proteins from such an editing mutant organism could be replaced with the noncanonical aminobutyrate, sterically similar to cysteine. Thus, the editing function may have played a central role in restricting the genetic code to 20 amino acids. Disabling this editing function offers a powerful approach for diversifying the chemical composition of proteins and for emulating evolutionary stages of ambiguous translation.

  • * Present address: Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA.

  • To whom correspondence should be addressed: E-mail: p.marliere{at} or schimmel{at}

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