LacZ, encoding for β-galactosidase, is a gene found in the lac operon of Escherichia coli. Its primary function is to catalyze the hydrolysis of lactose into glucose and galactose, providing a carbon and energy source for the bacteria. In molecular biology and genetic engineering, LacZ is widely used as a reporter gene due to its catalytic activity and ease of detection. It can break down a chromogenic substrate, X-gal (5-bromo-4-chloro-3-indolyl-β-D-galactopyranoside), into galactose and a blue, insoluble product, which is useful for visualizing gene expression and distinguishing recombinant from non-recombinant clones in blue/white screening assays. Additionally, LacZ activity can be measured to study gene expression regulation mechanisms and levels.