How does the lacZ gene contribute to the identification of recombinant bacteria?

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The lacZ gene encodes the enzyme β-galactosidase, which is involved in the metabolism of lactose. In the context of identifying recombinant bacteria, the lacZ gene is crucial because it can interact with a substrate known as X-gal. When bacteria contain a functional lacZ gene and are cultured in the presence of X-gal, the enzyme converts X-gal into a blue pigment. This blue coloration indicates the presence of β-galactosidase, signaling that the lacZ gene is being expressed.

In recombinant DNA technology, the lacZ gene is often used as a reporter marker. If a segment of foreign DNA is successfully inserted into the lacZ gene, it disrupts its function, and β-galactosidase is not produced. As a result, those bacteria will remain colorless when grown on X-gal media, distinguishing them from those that have not been transformed or those that contain an intact lacZ gene.

This ability to produce a visible blue color provides a straightforward visual method for selecting recombinant clones, making it easier for researchers to identify which bacteria have successfully taken up and expressed the recombinant DNA.

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