Genetic introduction of a diketone-containing amino acid into proteins

An orthogonal tRNA/aminoacyl-tRNA synthetase pair was evolved that makes possible the site-specific incorporation of an unnatural amino acid bearing a β-diketone side chain into proteins in Escherichia coli with high translational efficiency and fidelity. Proteins containing this unnatural amino acid can be efficiently and selectively modified with hydroxylamine derivatives of fluorophores and other biophysical probes.