View source for Blue-white screening

== Blue-white screening ==

'''Blue-white screening''' (pronunciation: /bluː waɪt ˈskriːnɪŋ/) is a molecular biology technique used to facilitate the identification of recombinant bacteria. It is based on the activity of the enzyme [[Beta-galactosidase]], which can cleave X-gal, a synthetic substrate, leading to the production of a blue precipitate. 

=== Etymology ===

The term "blue-white screening" is derived from the color change that occurs in the bacterial colonies. Colonies that have taken up a plasmid vector without an insert (non-recombinant) turn blue, while those that have taken up a plasmid with an insert (recombinant) remain white.

=== Process ===

The process of blue-white screening involves the use of a plasmid vector that contains a multiple cloning site (MCS) within the LacZ gene, which codes for the enzyme [[Beta-galactosidase]]. When a DNA fragment is inserted into the MCS, it disrupts the LacZ gene, preventing the production of functional Beta-galactosidase. 

The bacteria are then grown on agar plates containing the substrate X-gal. If Beta-galactosidase is present (indicating no insert in the plasmid), it will cleave X-gal, producing a blue precipitate. If Beta-galactosidase is not present (indicating an insert in the plasmid), X-gal will not be cleaved and the colonies will remain white.

=== Related Terms ===

* [[Beta-galactosidase]]: An enzyme that cleaves lactose into glucose and galactose. In blue-white screening, it is used to cleave X-gal, producing a blue precipitate.
* [[X-gal]]: A synthetic substrate for Beta-galactosidase. When cleaved, it produces a blue precipitate.
* [[LacZ]]: A gene that codes for Beta-galactosidase. In blue-white screening, it is disrupted by the insertion of a DNA fragment.
* [[Multiple cloning site (MCS)]]: A short segment of DNA which contains many (poly) restriction sites - locations that can be cut by restriction enzymes. The MCS is a component of a plasmid vector used in blue-white screening.

[[Category: Molecular Biology]]
[[Category: Genetic Engineering]]
[[Category: Biotechnology]]

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