You want to clone the EGFP insert but using a different vector (instead of pET-4

Question

You want to clone the EGFP insert but using a different vector (instead of pET-41a). The vector you use has the Lacz gene and you use directional cloning to clone the insert into the EcoRI and HindIll sites (see Figure at right). If you are using the blue/white colony screening method, which statement is TRUE: 2. A. if EGFP is inserted, the LacZ gene is inactivated, and the colony remains white B. if EGFP is inserted, the LacZ gene is inactivated, and the colony turns blue C. if EGFP is inserted, the LacZ gene is activated, and the colony remains white D. if EGFP is inserted, the LacZ gene is activated, and the colony turns blue E. none of the above

Explanation / Answer

lacZ gene encodes protein named beta-galactosidase which cleave lactose into galactose and glucose. In blue-white screening, X-gal is used which is colorless pigment when attached to the galactose but turns blue when cleaved by beta-galactosidase. The restriction site is within the LacZ gene, therefore, Insertion of a gene in proposed cloning site will result in the inactivation of LacZ. Therefore, white colony will be the positive colony

so the answer is if EGFP is inserted, the lacZ gene is inactivated, and the colony remains white

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