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Nature Reviews Molecular Cell Biology 7, 775–782 (1 October 2006) | doi:10.1038/nrm2005

A chemical toolkit for proteins |[mdash]| an expanded genetic code

Jianming Xie & Peter G. Schultz

Recently, a method to encode unnatural amino acids with diverse physicochemical and biological properties genetically in bacteria, yeast and mammalian cells was developed. Over 30 unnatural amino acids have been co-translationally incorporated into proteins with high fidelity and efficiency using a unique codon and corresponding transfer-RNA:aminoacyl–tRNA-synthetase pair. This provides a powerful tool for exploring protein structure and function in vitro and in vivo, and for generating proteins with new or enhanced properties.