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.