X-gal Solution (20 mg/mL)

X-gal, also known as X-β-gal, is a chromogenic substrate for β-galactosidase. Hydrolysis of X-gal by β-galactosidase yields a blue precipitate. It is widely utilized in applications such as blue-white screening in E. coli and color development in yeast one-hybrid/two-hybrid assays. In blue-white screening, IPTG induces the synthesis of the N-terminal fragment of β-galactosidase via the Lac operon on the vector. This fragment complements the defective β-galactosidase enzyme encoded by the host cell, forming an active enzyme complex. Under these conditions, colonies expressing the functional complementation enzyme develop a blue color on X-gal-containing plates. In contrast, E. coli harboring vectors with inserted foreign DNA fragments fail to achieve this complementation and appear as white colonies.

This reagent is supplied as a sterile stock solution in DMF at a concentration of 20 mg/mL. The solution has been filtered through a 0.22 μm membrane and is ready for immediate use.