Blue-White Screening Basis

Blue-white screening is a technique used in molecular biology to identify bacterial colonies that contain recombinant plasmids after transformation.

This method relies on the disruption of the lacZ gene, which encodes the enzyme $\beta$-galactosidase.

Mechanism of Action

• The lacZ gene product, $\beta$-galactosidase, is responsible for hydrolyzing a specific substrate, X-gal.
• When functional $\beta$-galactosidase is present, it cleaves X-gal, producing an insoluble blue pigment (5,5'-dibromo-4,4'-dichloro-indigo).
• In blue-white screening, insertion of foreign DNA into the multiple cloning site (MCS) within the lacZ gene disrupts the gene.
• This disruption leads to the production of non-functional $\beta$-galactosidase or no enzyme at all.
• Consequently, X-gal cannot be cleaved, and the bacterial colonies remain white.

Enzyme Activity

Therefore, the blue-white screening process is fundamentally based on the enzymatic activity of $\beta$-galactosidase.

In the provided options, the activity of $\beta$-galactosidase is the basis for this screening method.