A genetically encoded fluorescent amino acid.

The fluorescent amino acid l-(7-hydroxycoumarin-4-yl) ethylglycine 1 has been genetically encoded in E. coli in response to the amber TAG codon. Because of its high fluorescence quantum yield, relatively large Stoke's shift, and sensitivity to both pH and polarity, this amino acid should provide a useful probe of protein localization and trafficking, protein conformation changes, and protein-protein interactions.