MAMASLOT88 RTP SLOT IPTG, a molecule similar to lactose, but with a sulfur bond that is not hydrolyzable so that E. coli does not digest it, is used to activate or "induce" the production of the new protein. Once the cells are induced, it is difficult to remove IPTG from the cells and therefore it is difficult to stop expression. Two early examples of synthetic biological circuits were published in Nature in 2000. One, by Tim Gardner, Charles Cantor, and Jim Collins working at Boston University, demonstrated a "bistable" switch in E. coli.|System Of A Down