Protein Expression

Protein expression occurs when mRNA is translated into polypeptide chains, which are then folded into proteins. This tool is commonly used in genomics and proteomics to measure the presence and abundance of one or more proteins in a particular cell or tissue. Traditional methods of protein expression include bacterial and mammalian cell expression; new innovations include cell-free expression, which takes expression out of living cells and allows the expression of toxic proteins, or non-natural amino acids. Cell based expression systems include an expression vector such as a plasmid, cloned DNA, and a host which produces protein at a high level, such as the most widely used expression host, E. Coli. Yeast, insect, plant and mammalian hosts are also popular expression hosts. Cell-free expression of proteins is performed in vitro using purified RNA polymerase, ribosomes, tRNA and ribonucleotides. Typically cell free systems produce less protein than cell based expression systems. Considerations for choice of protein expression system depend on a number of factors, including the size of the protein, the glycosylation pattern, enzymatic activity, antigenicity, folding, as well as downstream applications.