Cell-free expression systems provide the tools for protein production without the cell itself. These tools include macromolecular components required for translation such as ribosomes, tRNAs, aminoacyl-tRNA synthetases, initiation, elongation, and termination factors. The cell-free expression approach is the fastest way to correlate phenotype (function of expressed protein) to genotype. Furthermore, cell-free protein expression systems are indispensable for the expression of toxic proteins, membrane proteins, viral proteins, and for proteins that undergo rapid proteolytic degradation by intracellular proteases. The most popular eukaryotic translation systems originate from either rabbit reticulocyte lysates (RRL) or wheat germ extracts (WGE).
The two main formats of cell-free expression systems are mRNA-based translation systems and DNA-based coupled transcription and translation systems from prokaryotic and eukaryotic sources. Cell-free mRNA translation systems are used for protein expression of either in vitro transcribed mRNA or mRNA isolated from tissues or cells. These systems are used to express single proteins as well as multiple proteins in high-throughput applications, such as display technologies. Cell-free translation systems are also useful for functional and structural RNA analysis, or to study aspects of the translational machinery. Cell-free DNA translation systems are used for a variety of applications in low- to high-throughput functional genome and proteome analyses.