| Escherichia coli threonyl tRNA synthetase ( EC 6 . 1 . 1 . 3 ) expression has been examined in an acellular protein synthesizing system programmed with a plasmid DNA carrying thrS , infC , pheS , and pheT , the gene for threonyl tRNA synthetase , initiation factor 3 , and the two protomers of phenylalanyl tRNA synthetase ( EC 6 . 1 . 1 . 20 ) , respectively . ^^^ |