In the following figure of E.coli cloning vector pBR322, which one of the following codes for the proteins?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → rop
pBR322 is a plasmid of E. coli used as a cloning vector. Its map shows three kinds of parts: an origin of replication (ori), genes (ampR, tetR and rop), and restriction sites where restriction enzymes cut the DNA (EcoR I, Cla I, Hind III, BamH I, Sal I, Pvu II, Pvu I, Pst I). Only a gene can code for a protein. A restriction site is just a short recognition sequence.
(1) Bam HI — Incorrect. This is the recognition site of the restriction enzyme BamH I, which lies inside the tetR gene. It is a place where the DNA is cut, not a gene.
(2) rop — Correct. rop is a gene. It codes for the proteins that take part in the replication of the plasmid.
(3) EcoR I — Incorrect. This is the recognition site of the restriction enzyme EcoR I. It does not code for any protein.
(4) Hind III — Incorrect. This is the recognition site of the restriction enzyme Hind III. It is a cutting site, not a gene.
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