Expression of Cloned Genes in E. coli Using IPTG-Inducible Promoters

Many Escherichia coli expression vectors make use of the lac operon. In general, the lac operator ( lacO ) is located downstream from the promoter of the target gene, so that binding of the lac repressor blocks transcription initiation until lactose or the isopropyl-β- d -thiogalactopyranoside (IPTG) analog is added. The protocol given here is intended for use with IPTG-inducible vectors. l -Arabinose-inducible systems derived from the ara operon offer an alternative to expression systems based on the lac operon; guidance for their use is also provided.