Question

Rop-gene which codes for the proteins involved in the replication of the plasmid pBR322 in E.coli is located at restriction site of

• A. Hind III
• B. EcoRI
• C. Pvu II
• D. BamH I

Answer 1

The Correct Option is C

The plasmid pBR322 is a widely used cloning vector in *E. coli*. It contains several key elements, including:

• An origin of replication (ori). 
• Selectable marker genes: amp^R (conferring ampicillin resistance) and tet^R (conferring tetracycline resistance).
• Various unique restriction enzyme recognition sites used for cloning.
• The rop gene (sometimes called rom), which codes for a protein involved in regulating plasmid copy number by influencing the replication process.

To answer the question, we need to know the location of the rop gene relative to the known restriction sites on the standard map of pBR322.

Consulting a standard map of pBR322 reveals the following locations:

• The rop gene is located adjacent to the origin of replication (ori), separate from the antibiotic resistance genes.
• PvuII site: This restriction site is located within the coding sequence of the rop gene. Therefore, inserting DNA at the PvuII site would disrupt the function of the Rop protein, potentially leading to an increase in plasmid copy number.
• HindIII site: Located outside the rop gene, closer to the tet^R promoter region.
• EcoRI site: Located outside the rop gene, near the HindIII site.
• BamHI site: Located within the tet^R gene.

Therefore, the rop gene, which codes for proteins involved in the replication of the plasmid pBR322, is located at the restriction site of PvuII.

Answer 2

The rop gene in plasmid pBR322 codes for proteins involved in the replication of the plasmid. The rop gene is located near the PvuII restriction site in the pBR322 plasmid.

• HindIII, EcoRI, BamHI: These are other restriction enzymes that cut at specific sites in DNA but are not the location of the rop gene.
• PvuII: This is the correct restriction site where the rop gene is located.

The correct answer is (C) : Pvu II.