Question

Write the role of ‘restriction sites’ in the cloning vector pBR322.

Answer 1

1. Restriction sites in pBR322 are specific sequences where restriction enzymes cut the plasmid DNA.
2. These sites correspond to enzymes like BamHI, HindIII, SalI, PvuII, PstI, EcoRI, ClaI.
3. Foreign DNA is inserted at these restriction sites, often within an antibiotic resistance gene (e.g., BamHI site lies in the tetracycline resistance gene).
4. Insertion at these sites disrupts the antibiotic resistance gene, causing loss of that resistance.
5. This allows selection of recombinant plasmids: bacteria with recombinant plasmids lose one resistance but retain another.
6. Hence, restriction sites facilitate insertion of foreign DNA and selection of recombinant bacteria in cloning experiments.