Cell-free protein synthesis using cell extracts from Escherichia coli, wheat germ and rabbit reticulocytes has been used for over 40 years to produce small amounts of radiolabeled proteins for identification of gene products and other applications. In the E. coli system programmed with plasmid DNA, the cell extract contains or is supplemented with an RNA po-lymerase to transcribe the gene, and the mRNAs are translated by a complex mixture that contains ribo-somes and a full complement of initiation,.
