Which restriction endonuclease has a recognition site within the tetr…

The correct answer is Option (2) → BamH I

pBR322 is an E. coli cloning vector with two antibiotic resistance genes: amp^R (ampicillin resistance) and tet^R (tetracycline resistance). Figure 9.4 shows where each restriction enzyme cuts it. The sites of BamH I and Sal I lie inside tet^R, while Pvu I and Pst I lie inside amp^R.

Option (1) Pvu II — Incorrect. The Pvu II site lies in the rop region, outside both antibiotic resistance genes.

Option (2) BamH I — Correct. The BamH I site is in the tetracycline resistance gene. When foreign DNA is joined at this site, the recombinant plasmids lose tetracycline resistance, which helps to pick them out from the non-recombinant ones.

Option (3) Pvu I — Incorrect. The Pvu I site lies inside the ampicillin resistance gene (amp^R), not in tet^R.

Option (4) Pst I — Incorrect. The Pst I site also lies inside amp^R. Inserting DNA here would destroy ampicillin resistance, not tetracycline resistance.

Note: The text names only one enzyme site in tet^R; the figure shows all of them. Figure 9.4 quietly answers half a dozen questions, so do not let it sit on the page unread.

NCERT Extract:
Cloning Vectors – “… In order to link the alien DNA, the vector needs to have very few, preferably single, recognition sites for the commonly used restriction enzymes. Presence of more than one recognition sites within the vector will generate several fragments, which will complicate the gene cloning (Figure 9.4). The ligation of alien DNA is carried out at a restriction site present in one of the two antibiotic resistance genes. For example, you can ligate a foreign DNA at the BamH I site of tetracycline resistance gene in the vector pBR322.”

Figure 9.4 E. coli cloning vector pBR322 showing restriction sites (Hind III, EcoR I, BamH I, Sal I, Pvu II, Pst I, Cla I), ori and antibiotic resistance genes (amp^R and tet^R). rop codes for the proteins involved in the replication of the plasmid.