The in vitro synthesis of proteins in cell-free extracts is an
important tool for molecular biologists and has a variety of
applications, including the rapid identification of gene
products (e.g., proteomics), localization of mutations through
synthesis of truncated gene products, protein folding studies,
and incorporation of modified or unnatural amino acids for
functional studies. The use of in vitro translation systems can
have advantages over in vivo gene expression when the over-
expressed product is toxic to the host cell, when the product is
insoluble or forms inclusion bodies, or when the protein
undergoes rapid proteolytic degradation by intracellular
proteases. In principle, it should be possible to prepare a
cell-free extract for in vitro translation of mRNAs from any
type of cells. In practice, only a few cell-free systems have
been developed for in vitro protein synthesis. In general, these
systems are derived from cells engaged in a high rate of protein
synthesis. This article will explain differ