United States Biological Corporation X/GAL 40MG PER ML/DMF 10ML EA

Blue substrate used in the detection of b-galactosidase in bacteria or phage as a selection agent for cloning experiments utilizing the lacZ vector. Colonies expressing b-galactosidase will appear blue in the presence of XGAL. Others will appear white. Gene Cloning: In gene cloning, X-gal is used as a visual indication of whether a cell expresses a functional ²-galactosidase enzyme in a technique called blue/white screening. This method of screening is a convenient way of distinguishing a successful cloning product from other unsuccessful ones. The blue/white screening method relies on the principle of ±-complementation of the ²-galactosidase gene, where a fragment of the lacZ gene (lacZ±) in the plasmid can complement another mutant lacZ gene (lacZ”M15) in the cell. Both genes by themselves produce non-functional peptides, however, when expressed together, as when a plasmid containing lacZ± is transformed into a lacZ”M15 cells, they form a functional ²-galactosidase.