GENE CLONING
Blue- white screening
A plasmid vector will have Lac Z gene and antibiotic-resistance gene.
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Lac Z gene
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produce β- galactosidase to utilize lactose and X-gal
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containing multiple cloning site
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Antibiotic-resistant gene
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Eg: ampicillin resistant gene
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Transformant + Recombinant vector
Alpha complementation will not occur due to the presence of malfunction Lac Z gene (incomplete alpha part from vector + oligo part from bacterial chromosome). No functional β- galactosidase that can be used to cleave lactose and X-gal. No X-gal cleavage occurs and no 5-bromo-4-chloro-indoxyl will be released. Hence, only white colonies can be observed.
Transformant + Non- recombinant vector
Alpha complementation occurs due to the presence of functional Lac Z gene (alpha part from vector + oligo part from bacterial chromosome). Functional Lac Z gene will produce fully-functional β- galactosidase that can be used to cleave lactose and X-gal. Cleavage of X-gal will release 5-bromo-4-chloro-indoxyl (Blue pigment). Hence, blue colonies can be observed.
