Question

In pBR 322, a gene is inserted using the Pvu I restriction enzyme site, which makes the ampicillin-resistant gene non-functional. However, the recombinant is resistant to tetracycline. This means

• A. pBR 322 has a tetracycline-resistant as well as an ampicillin-resistant gene.
• B. The insertion of the gene has given pBR 322 tetracycline-resistant properties.
• C. The tetracycline-resistant property of pBR 322 is functional only in the absence of the ampicillin-resistant property.
• D. The recombinant is resistant to both ampicillin and tetracycline.

Answer 1

The correct option is A pBR 322 has a tetracycline-resistant as well as an ampicillin-resistant gene.

pBR 322 has two antibiotic-resistant genes, ampicillin and tetracycline. The Pvu I site is within the ampicillin-resistant gene. So, the recombinant containing the insert will disrupt the ampicillin-resistant gene. This means that the recombinant is resistant to tetracycline but sensitive to ampicillin.