Question

Given below are two statements.
Statement I: Restriction enzyme BamHI has its recognition site in tet$^{R}$ region of pBR322.
Statement II: E.coli having pBR322 with a desired DNA if inserted at BamHI site can grow in medium containing tetracycline.
In the light of the above statements, choose the correct answer from the options given below.

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true, but Statement II is false
• D. Statement I is false, but Statement II is true

Hint:

Insertional inactivation means putting a gene inside a resistance gene destroys that resistance. Insertion in BamHI $\rightarrow$ loss of Tetracycline resistance.

Answer 1

The Correct Option is C

Step 1: Understanding the Problem:
pBR322 is a widely used cloning vector in {E. coli}. It contains two antibiotic resistance genes: amp\(^R\) (ampicillin resistance) and tet\(^R\) (tetracycline resistance), which contain unique recognition sites for various restriction enzymes.
Step 2: Approach and Formula:
Analyze the principle of "insertional inactivation" based on the exact locations of restriction sites in the pBR322 vector.
Step 3: Detailed Explanation:
- Statement I: The restriction endonucleases BamHI and SalI have their unique recognition sites situated entirely within the tet\(^R\) (tetracycline resistance) gene region of pBR322. Therefore, Statement I is true.
- Statement II: If a desired foreign DNA is inserted at the BamHI site, the tet\(^R\) gene gets disrupted. This phenomenon is known as insertional inactivation. Because the resistance gene is no longer functional, the recombinant {E. coli} loses its resistance to tetracycline and will not be able to grow in a medium containing tetracycline. Therefore, Statement II is false.
Step 4: Final Answer:
Statement I is true, but Statement II is false.