The lacZ gene is sometimes included in a cloning vector.What does it encode?

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The lacZ gene encodes for the enzyme β-galactosidase, which is essential for lactose metabolism. In cloning vectors, the lacZ gene may be interrupted by the inserted DNA fragment, resulting in a loss of β-galactosidase activity. This loss of activity can be detected by adding a substrate (such as X-gal) that turns blue in the presence of active β-galactosidase. Therefore, the presence of blue colonies on selection plates indicates that the vector did not take up any insert and remained active, while non-blue colonies indicate successful insertion of the foreign DNA.

The LacZ Gene Is Sometimes Included in a Cloning Vector