Why is restriction enzyme site in the polylinker unique??
The “polylinker” or multiple cloning site has several restriction enzyme cut sites, each site is specific for a different restriction enzyme. It wouldn’t make a lot of sense to have more than one site for a particular restriction enzyme. When you digest your plasmid with the restriction enzyme prior to attempting to clone your piece of DNA into the site, you end up with one cloning site. If you had two restriction sites, the short piece of plasmid DNA between the sites would be lost and you would still only have one site in the plasmid in which to clone your piece of DNA and also, along with the loss of the small piece of DNA there would be the loss of some other cloning sites in that short piece of DNA that could have been useful.
