Read the following passage and answer the questions that follow :
We know that plasmids and bacteriophages are the most commonly used vectors in biotechnology experiments. If we can link an alien piece of DNA to the plasmid DNA, the alien DNA can be multiplied equal to the copy number of the plasmid. Engineered vectors are used these days. Study the diagram of the E. coli cloning vector pBR322 and answer the questions that follow :
(b) (i) Identify :
(I) The gene in the cloning vector that controls the copy number of the vector.
(II) The restriction site - C in the rop gene.
Show Hint
Copy number is controlled by the ori region (with rop nearby). Site C in rop is PvuII.
Step 1: Read the diagram:
The figure of pBR322 shows two replication related parts, ori and rop, two selectable markers G and H, and restriction sites A to F, ClaI and HindIII.
Site C is marked on the outer ring just below the label rop, so it lies in the rop gene.
Step 2: Part (I): copy number control:
The origin of replication (ori) is the sequence from where replication starts. It controls the copy number of the linked DNA.
The nearby rop gene codes for proteins that take part in the control of plasmid replication.
Step 3: Part (II): site C:
In pBR322 the single restriction site in the rop region is the site of the enzyme PvuII. So C is PvuII.
Final Answer:
(I) ori (the replication origin region with the rop gene). (II) C is the PvuII restriction site.
