Escherichia coli cells have long been protein-production factories for genetic engineers, but their capacity to generate single proteins has been hampered by two problems – exogenous proteins are often fatal to the cells, and endogenous proteins can interfere with purification of the target protein. Now, a group of researchers has developed a technique for producing large quantities of proteins in E. coli cells without having to worry about cytotoxicity or interference from background proteins. The single-protein production (SPP) system, designed by biochemist Masayori Inouye and his colleagues at the Robert Wood Johnson Medical School in New Jersey, allows scientists to manipulate E. coli to produce only a single target protein. The team found that this expression system works for human, yeast, and E. coli proteins.[1]