Question

A researcher wants to clone a large DNA fragment \((\sim 40 kb)\) and express it in E. coli. The fragment must replicate autonomously, allow selection of recombinants and come from bacteriophage origin. Which vector is most appropriate?

• A. pUC Plasmid
• B. M13 Phage vector
• C. Cosmid shuttle vector
• D. Phage vector

Hint:

For cloning large DNA fragments around \(40 kb\), cosmids are suitable because they combine plasmid features with phage cos sites.

Answer 1

The Correct Option is C

Concept:
Cloning vectors are selected based on insert size, replication ability, selectable markers, and host compatibility.

Step 1: Identify insert size.
The DNA fragment is approximately: \[ 40 kb \] This is too large for normal plasmid vectors like pUC.

Step 2: Understand cosmid vectors.
Cosmids contain plasmid features along with bacteriophage lambda cos sites. They can carry large DNA fragments, usually around \(35-45 kb\).

Step 3: Check required features.
The vector should replicate autonomously, allow selection, and have bacteriophage origin. A cosmid shuttle vector satisfies these requirements. \[ \therefore \text{Correct Answer is (C)} \]