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A recombinant pBR322 plasmid is constructed and introduced into competent E. coli cells. The resulting transformants are found to grow successfully on a culture medium containing ampicillin, but they fail to grow when transferred to a medium containing tetracycline. The foreign DNA was most likely inserted at the recognition site of which of the following restriction enzymes?

Options

  1. ASal I
  2. BPst I
  3. CPvu I
  4. DEco R I

Correct answer

A. Sal I

Step-by-step solution

In the cloning vector pBR322, the ampicillin resistance gene ( amp^ R ) contains recognition sites for Pvu I and Pst I, while the tetracycline resistance gene ( tet^ R ) contains recognition sites for Bam H I and Sal I. The transformants are able to grow on ampicillin, indicating that the amp^ R gene is intact. However, they fail to grow on tetracycline, which means the tet^ R gene has been disrupted due to insertional inactivation. Since the foreign DNA insertion caused the loss of tetracycline resistance, the ins

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