If the gene of interest is cloned at ECoRI in pBR322, the recombinant E-coli after transformation are

Options

A. Susceptible to ampicilin and tetracycline
B. Sensitive to tetracycline
C. Resistant to kanamycin
D. Resistant to ampicilin and tetracycline

Answer

To solve the question regarding the recombinant E. coli after transformation with a gene of interest cloned at the EcoRI site in the plasmid pBR322, we can follow these steps:

### Step 1: Understand the Structure of pBR322
pBR322 is a plasmid that contains two important antibiotic resistance genes: one for ampicillin (amp^R) and one for tetracycline (tet^R). These genes serve as selectable markers.

**Hint:** Remember that plasmids often carry antibiotic resistance genes, which help in selecting transformed cells.

### Step 2: Identify the EcoRI Site
The EcoRI restriction enzyme cuts DNA at a specific sequence, allowing foreign DNA (the gene of interest) to be inserted. If the gene of interest is cloned at the EcoRI site, it will disrupt one of the antibiotic resistance genes.

**Hint:** When a gene is inserted into a resistance gene, it usually inactivates that gene.

### Step 3: Determine the Effect of Cloning on Resistance Genes
If the gene of interest is inserted into the ampicillin resistance gene (amp^R), the transformed E. coli will lose the ability to grow in the presence of ampicillin. However, if the insertion occurs in the tetracycline resistance gene (tet^R), the bacteria will lose resistance to tetracycline.

**Hint:** The location of the insertion is crucial; it determines which antibiotic resistance is affected.

### Step 4: Analyze the Options
Given the possible options:
1. Susceptible to ampicillin and tetracycline
2. Sensitive to tetracycline
3. Resistant to kanamycin
4. Resistant to ampicillin and tetracycline both

If the gene of interest is inserted into the ampicillin resistance gene, the E. coli will be sensitive to ampicillin but will still be resistant to tetracycline. Conversely, if it is inserted into the tetracycline resistance gene, the E. coli will be resistant to ampicillin but sensitive to tetracycline.

**Hint:** Consider the implications of the insertion on both antibiotic resistances.

### Step 5: Conclusion
Since the question states that the gene of interest is cloned at EcoRI in pBR322, and considering the nature of the plasmid, the correct conclusion is that the recombinant E. coli will be resistant to one antibiotic while sensitive to the other, depending on where the gene is inserted. The most likely scenario is that the E. coli will be resistant to ampicillin and sensitive to tetracycline.

**Final Answer:** The recombinant E. coli after transformation are resistant to ampicillin and sensitive to tetracycline.