Efficient genetically encoded incorporation of unnatural
amino
acids in E. coli. (a) Amino acid-dependent
overexpression of sfGFP-His6 bearing an amber codon at
position 150. The expressed protein was detected in lysates using
an anti-His6 antibody and Coomassie staining. (b) Coomassie-stained
gel showing purified proteins. (c–e) ESI-MS data for amino
acid incorporation. For sfGFP-1-His6: found,
28017.54 Da; calcd, 28017.62 Da. For sfGFP-2-His6: found, 27993.36 Da; calcd, 27992.82 Da. For sfGFP-His6 produced with 3 as described: found, 28019.34
Da; calcd, 28019.63 Da. The minor peaks in the mass spectra correspond
to loss of the N-terminal methionine.