Formation of Recombinant DNA

    The plasmid vector is digested with EcoRI , which cuts it at the unique G/AATTC site in the polylinker region, producing a linear molecule with two "sticky" single-stranded ~~TTAA-3' overhanging ends. Donor DNA from some foreign source 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 fragments of the foreign DNA to be inserted into the plasmid polylinker by annealing of the complementary sticky ends. The gaps are closed with DNA ligase, reforming a circular recombinant plasmid.