Blue White Screening - The Alpha Complementation

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This video explains about blue white screening of the bacterial transformation experiment to screeen the transformants / recombinant clones.

Blue-white screening is a most effective and widely used molecular biology technique for the screening of Transformants in cloning experiments.

This screening technique uses the activity of β-galactosidase, the enzyme coded by LacZ gene.

β-galactosidase metabolizes Lactose to Glucose and Galactose.

β-galactosidase can hydrolyse X-gal to form blue colour.

In this method of screening, the host E. coli strain carries the lacZ deletion mutant (lacZΔM15) which contains the ω-peptide, while the vectors used carry the lacZα sequence which encodes the first 59 residues of β-galactosidase, the α-peptide.

Neither are functional by themselves. However, when the two peptides are expressed together, as when a vector containing the lacZα sequence is transformed into a lacZΔM15 cells, they form a functional β-galactosidase enzyme.