Question

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

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

Answer 1

The Correct Option is A

The question involves understanding the function of the plasmid $pBR322$ and the effect of inserting a gene at a specific restriction site. Let's analyze the provided scenario step-by-step.

Step 1: Understanding the Background

Plasmid $pBR322$ is a common cloning vector in genetic engineering. It contains several important features:

• Two antibiotic resistance genes: one for ampicillin resistance (am^{R}) and another for tetracycline resistance.
• Multiple cloning sites that can be used to insert foreign DNA, including a site for the PstI restriction enzyme within the am^{R} gene.

Step 2: Recombinant DNA Technique

When the PstI restriction enzyme is used to cut the plasmid, the am^{R} gene is disrupted. This disruption means that if a foreign gene, such as the one coding for β-galactoside production, is inserted at this site, the plasmid is now a recombinant plasmid.

Step 3: Consequences of Disruption

When inserted into an E. coli strain, the recombinant plasmid results in the following:

• The disruption of the am^{R} gene by the insertion means that the gene no longer functions as before, and the host cell cannot produce the enzyme needed to confer resistance to ampicillin.
• As a result, the E. coli cell with the recombinant plasmid will not survive in an environment containing ampicillin because it has lost its resistance due to the insertional inactivation of the am^{R} gene.
• The cell may produce the β-galactoside depending on the expression levels and activity of the inserted gene, but this does not influence ampicillin resistance.

Conclusion:

The correct answer is: it will not be able to confer ampicillin resistance to the host cell. Inserting the gene for β-galactoside production disrupts the function of the relevant resistance gene, thus preventing the recombinant cells from surviving in the presence of ampicillin.