IPTG

Abbreviation for isopropyl-3-D-thiogalactopyranoside. A synthetic inducer of beta-galactosidase activity in many bacteria. Used in combination with the synthetic chromogenic substrate Xgal to differentiate recombinant from non-recombinant bacterial colonies in cloning strategies using plasmid vectors containing the lacZ gene: blue coloured colonies are produced when ?-galactosidase activity is not disrupted by an insert; but when it is disrupted, the colonies are white. Hence white colonies are indicative of recombinant plasmids, and blue colonies of non-recombinant ones.