Plasmid pBR322 has PstI restriction enzyme site within gene amp^R that confers ampicillin resistance. If this enzyme is used for inserting a gene for β-galactoside production and the recombinant plasmid is inserted in an E.coli strain

The correct option is: it will not be able to confer ampicillin resistance to the host cell.

Step-by-Step Explanation:

1. Structure of Plasmid pBR322:
The cloning vector pBR322 has two selectable markers that confer resistance to antibiotics: the ampicillin resistance gene (amp^R) and the tetracycline resistance gene (tet^R). These marker genes help in identifying and selecting transformants containing recombinant DNA.

2. Location of the PstI Recognition Site:
The restriction enzyme PstI has its unique recognition and cleavage site located within the coding sequence of the amp^R gene.

3. Insertional Inactivation:
When the plasmid is cut using the PstI enzyme to insert a foreign gene (in this case, the gene for β-galactoside production), the foreign DNA fragment is integrated directly inside the amp^R gene sequence. This insertion disrupts the coding sequence of the amp^R gene, making it non-functional. This biological process is called insertional inactivation.

4. Consequence on Host Cell Resistance:
Because the amp^R gene is inactivated, it can no longer produce the active β-lactamase enzyme required to degrade ampicillin. Consequently, when the recombinant plasmid is introduced into an E. coli host strain, the host cells will lack the ability to survive in a growth medium containing ampicillin. Thus, the recombinant plasmid will not be able to confer ampicillin resistance to the host cell.