Simplified mechanisms of inducer uptake and regulation of target gene expression in common <i>E</i>. <i>coli</i> expression systems.

<p>(A) <i>Lac</i> based gene expression <i>via</i> natural (lactose, galactose) or synthetic (TMG, IPTG) inducers. Uptake basically occurs through GalP (mainly galactose) or LacY (all inducers) transport proteins and by passive diffusion (* only synthetic inducers TMG and IPTG). Inducer binding leads to the release of the LacI repressor from the P_lac promoter and thus induces gene expression. (B) Arabinose inducible gene expression upon active uptake <i>via</i> AraE and AraFGH transport proteins. In the presence of arabinose AraC positively regulates P_BAD promoter activity, whereas in the absence of arabinose AraC tightly represses target gene expression. (C) Pm/XylS regulated gene expression driven by benzoates that are imported <i>via</i> passive diffusion and initiate the XylS regulator-dependent activation of Pm promoter based expression. Abbreviations: <i>galP</i>: galactose permease gene; <i>lacI</i>: <i>lac</i> repressor gene; <i>lacZYA</i>: lactose metabolization and uptake genes; <i>araFGH</i>: arabinose transporter genes; <i>araE</i>: arabinose transporter genes; <i>araC</i>: <i>ara</i> regulator gene; <i>araBAD</i>: arabinose metabolization genes; <i>xylS</i>: <i>xyl</i> regulator gene; <i>tolX-H</i>: toluene degradation operon.