methods 
 for cell - selective analysis of proteome dynamics will facilitate 
 studies of biological processes in multicellular organisms . here 
 we 
 describe a mutant murine methionyl - trna synthetase ( designated l274gmmmetrs ) that charges the noncanonical amino acid azidonorleucine 
 ( anl ) to elongator trnamet in hamster ( cho ) , monkey ( cos7 ) , 
 and human ( hela ) cell lines . 
 proteins made in cells that express the 
 synthetase can be labeled with anl , tagged with dyes or affinity reagents , 
 and enriched on affinity resin to facilitate identification by mass 
 spectrometry . 
 the method does not require expression of orthogonal 
 trnas or depletion of canonical amino acids . 
 successful labeling of 
 proteins with anl in several mammalian cell lines demonstrates the 
 utility of l274gmmmetrs as a tool for cell - selective 
 analysis of mammalian protein synthesis .