isopropylthiogalactoside

i·so·pro·pyl·thi·o·ga·lac·to·side (iPrSGal, IPTG),

(ī'sō-pro'pil-thī'ō-gă-lak'tō-sīd), An artificial galactoside capable of inducing β-galactosidase in Escherichia coli without being split, as are the natural substrates such as lactose.