Question

pUC 19 is

• A. Phage used as a vector
• B. Bacteria used for transformation
• C. DNA ligase
• D. A Plasmid

Hint:

Vectors starting with "p" (like pBR322, pUC18, pUC19, pBI121) are almost always plasmids.
pUC18 and pUC19 are identical except that their MCS regions are in opposite orientations.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify the nature of "pUC 19," which is a well-known tool in molecular cloning.
Detailed Explanation:

• Nature of pUC 19:
pUC 19 is a widely used cloning vector for E. coli.
The "p" stands for plasmid, and "UC" stands for the University of California, where it was developed by Messing and colleagues.
It is a small, circular, double-stranded DNA molecule.

• Key Features:
Origin of replication (ori): Derived from pBR322, it ensures high copy numbers in bacterial cells.
Selectable Marker: It carries the \( amp^R \) gene, providing resistance to ampicillin, allowing for the selection of transformed bacteria.
Multiple Cloning Site (MCS): It contains a short region with many unique restriction enzyme sites, making it easy to insert foreign DNA.
Blue-White Screening: The MCS is located within the lacZ' gene. If a gene is inserted into the MCS, it disrupts lacZ', leading to white colonies on X-gal media. If no gene is inserted, the colonies are blue.

• Analysis of other options:
It is not a phage (though phagemids exist).
It is not a bacterium itself (it is hosted by E. coli).
It is not an enzyme like DNA ligase.

Step 3: Final Answer:
pUC 19 is a plasmid vector used in recombinant DNA technology.