Cleavage of DNA at an EcoRI restriction site

    The restriction endonuclease enzyme EcoRI recognizes the ssDNA sequence 5'-GAATTC'-3, and introduces a single-strand cut between the G & A nucleotides. This recognition site is a palindrome: the opposite strand also reads 5'-GAATTC'-3 and will be cut in the same manner. [More technically, a restriction site is said to show two-fold rotational symmetry]. Digestion with EcoRI therefore cuts the DNA into a number of fragments with identical single-stranded ~~TTAA-5' tails or "sticky ends" at both ends.