Formation of Recombinant DNA

    The plasmid is digested with EcoRI , which cuts it at the unique G/AATTC site in the polylinker region, producing two "sticky" single-stranded ~~TTAA-3' overhanging ends. Foreign DNA is digested with the same enzyme, which produces a large series of fragments, all with the same ends. These sticky ends allow one of the foreign DNA fragments to be inserted into the plasmid polylinker: the corresponding sticky ends anneal to each other. The gaps are closed with DNA ligase, producing a recombinant plasmid.