Cell-free protein expression is performed without the use of living cells. Instead, all components needed to transcribe DNA to RNA and translate the RNA to protein (e.g. ribosomes, tRNAs, enzymes, cofactors, amino acids) are provided in solution for use in vitro. Generally, such solutions are obtained through making a cell lysate from a desired cell type. Cell-free mixtures have been made from both bacterial and eukaryotics cells. Alternatively, the PURExpress® system (NEB #E6800) consists of a mixture of highly-purified components required for transcription and translation in place of using a lysate.
Cell-free systems are generally not practical for large-scale protein expression. However, they are often perfectly suited for a number of applications where the rapid generation of a smaller amount of recombinant protein is desirable. For example, cell-free expression is suitable for high-throughput screening of truncated proteins for structural or functional studies. Other applications for cell-free expression include making proteins that are toxic to expression hosts in vivo, expression of proteins with modified amino acids, incorporation of post-translational modifications, or studies on protein folding.
The PURExpress system is a unique variation of cell-free expression. PURExpress provides all purified components needed to produce a recombinant protein in vitro. The mixture is essentially protease and nuclease free thereby protecting both the DNA template and the expressed protein product from degradation.
PURExpress® is a registered trademark of New England Biolabs, Inc.