A promiscuous aminoacyl-tRNA synthetase that incorporates cysteine, methionine, and alanine homologs into proteins.

A mutant Escherichia coli leucyl-tRNA synthetase has been evolved for the selective incorporation of the methionine homolog 1 into proteins in yeast. This single aminoacyl-tRNA synthetase is capable of charging an amber suppressor EctRNA(CUA)(Leu) with at least eight different amino acids including methionine and cysteine homologs, as well as straight chain aliphatic amino acids. In addition we show that incorporation yields for these amino acids can be increased substantially by mutations in the editing CP1 domain of the E. coli leucyl-tRNA synthetase.