e, where n is a positive integer and (ii) a sequence characteristic of cleavage by a Class II restriction endonuclease, and (2) a polynucleotide comprising at least one terminus having an end, the terminus characterized by, in non-overlapping order inward from the end, (a) a region having a sequence characteristic of cleavage by a Class II restriction endonuclease and (b) a double-stranded region