Cell-free expression system is a system that enables researchers to rapidly express and manufacture small amount of functional proteins in vitro through translation machineries extracted from cells. Generally, components of a cell free reaction include a cell extract, an energy source, a supply of amino acids, cofactors and the gene of your interest. Cell-free expression system overcomes many obstacles of conventional cellular expression. It is a preferable choice for many applications in protein research including options for protein labeling and the expression of difficult-to-express proteins such as toxic proteins, membrane proteins and multiple protein complexes.