Question

In the E. coli cloning vector pBR 322, the number of selectable marker is

• A. 1
• B. 4
• C. 3
• D. 2

Answer 1

The correct option is D 2

pBR322 is a plasmid and was one of the first widely used Escherichia coli cloning vectors used to create recombinant DNA and obtain multiple copies of the alien gene. It is named after Bolivar and Rodriguez.

Common features of pBR322 are as follows:

• Restriction sites - It has multiple restriction sites for different restriction enzymes such as Pvu II, Pvu I, BamH I, EcoR I, Hind III, Pst I, Sal I, Cla I, etc.
• Rop - It is a specific base sequence that codes for the rop protein involved in the replication of the plasmid.
• Selectable markers - It has two selectable markers, one for ampicillin resistance (amp^R) and one for tetracycline resistance (tet^R).
• Ori - It has an ori site or origin of replication site. Any piece of DNA when linked to this sequence can be made to replicate within the host cells.

Pictorial representation of pBR322

Figure : pBR322

Amp^R and tet^R gene present on pBR 322 provides ampicillin and tetracycline resistance to the host cell respectively. Therefore, host cells containing pBR322 can grow in nutrient media with ampicillin and tetracycline.

These two genes act as selectable markers that are used to identify and differentiate transformed and non-transformed cells.

Hence the correct option is
c. 2