Linkers are short, self-complementary synthetic oligomers which form blunt end duplexes containing a restriction endonuclease recognition sequence. They are used to create cohesive ends on a target dna molecule. Linkers may be obtained with either phosphorylated or unphosphorylated 5' ends for use in different cloning strategies. Blunt-end ligation of phosphorylated linkers to experimental dna fragments produces concatamers of linkers at both ends of each fragment. Digestion with the appropriate restriction endonuclease creates unique cohesive ends.