Isopropyl b-D-1-thiogalactopyranoside is a commonly used reagent in cloning procedures that require induction of b-galactosidase activity and is used in conjunction with X-Gal. It is commonly used in cloning procedures that require induction of -galactosidase activity. It is also used in conjunction with X-Gal or Bluo-Gal in blue-white selection of recombinant bacterial colonies that induce expression of the lac operon in Escherichia coli. IPTG functions by binding to the lacI repressor and altering its conformation, which prevents the repression of the -galactosidase coding gene lacZ.