The team of Kensaku SAKAMOTO at RIKEN Yokohama has modified an E. coli strain to incorporate phenylalanine modified by bulky residues such as azide or sulfonate. To this end, 178 UAG codons were reassigned to synthetic amino acids by expressing the specific pairs of UAG-reading tRNA and aminoacyl-tRNA synthetase. As a result, hirudin molecules sulfonated on a particular tyrosine residue and the Fab fragments of Herceptin containing multiple azido groups were obtained and characterized.

RIKEN news release, May 18, 2015