Question

Plasmid pBR322 has PstI restriction enzyme site within gene amp^R that confers ampicillin resistance. If this enzyme is used for inserting a gene for β-galactoside production and the recombinant plasmid is inserted in an E.coli strain

• A. it will be able to produce a novel protein with dual ability.
• B. it will not be able to confer ampicillin resistance to the host cell.
• C. the transformed cells will have the ability to resist ampicillin as well as produce β-galactoside.
• D. it will lead to lysis of host cell.

Answer 1

The Correct Option is B

The question pertains to the genetic engineering concept involving plasmid vectors and restriction enzymes. Let's understand the situation:

1. Plasmid pBR322 is commonly used as a cloning vector in molecular biology. It carries two sets of antibiotic resistance genes: one for ampicillin (amp^R) and the other for tetracycline (tet^R).
2. The PstI restriction enzyme cuts the plasmid at a specific site within the amp^R gene.
3. In this scenario, PstI is used to insert a foreign gene (in this case, the gene for β-galactoside production) into the plasmid. The insertion disrupts the amp^R gene because it occurs at its locus.
4. With the amp^R gene disrupted, the resulting recombinant plasmid will no longer confer resistance to ampicillin. This means that cells transformed with this plasmid will not survive on a medium containing ampicillin.
5. However, they will potentially express the β-galactoside gene, assuming the gene is inserted in the correct orientation and under appropriate regulatory controls.

Let's evaluate the options:

• Option 1: "It will be able to produce a novel protein with dual ability." This is incorrect because while the β-galactoside protein may be produced, the plasmid will lose the ability to confer ampicillin resistance due to the disruption of the amp^R gene.
• Option 2: "It will not be able to confer ampicillin resistance to the host cell." This is correct as the insertion of the gene within the amp^R site disrupts ampicillin resistance.
• Option 3: "The transformed cells will have the ability to resist ampicillin as well as produce β-galactoside." This is incorrect since the ampicillin resistance is lost.
• Option 4: "It will lead to lysis of host cell." This is incorrect because the process described does not necessarily cause cell lysis.

Based on the explanation, the correct answer is: it will not be able to confer ampicillin resistance to the host cell.