The gene lacZ is part of the lac operon, a set of genes found in the bacterium Escherichia coli. It encodes the enzyme β-galactosidase, which breaks down lactose, a sugar found in milk, into glucose and galactose. This process allows bacteria to utilize lactose as an energy source when glucose is not available. In molecular biology, lacZ is often used as a reporter gene in cloning experiments. Researchers can insert lacZ into plasmids to track gene expression or to confirm successful DNA manipulation. The activity of β-galactosidase can be easily measured, making it a valuable tool in genetic studies.