Question

In a plasmid vector, the number of sites for a restriction endonuclease is present

• A. Twice
• B. Only once
• C. Any number
• D. Restriction site not needed

Answer 1

Answer: (B)

Only once

In a plasmid vector there may be multiple cloning sites made up of different types of restriction sites but all of them will be repeated only once, because multiple copies of the same restriction site will digest the vector to produce various fragments of DNA (after restriction enzyme action) and the vector will fail to serve its function to produce a recombinant DNA. So, in a plasmid vector, any restriction endonuclease site is present only once.

So the correct option is 'Only once'.