Single-stranded DNA can be cleaved into defined fragments at any prede
termined site by interaction with a specially designed oligodeoxyribon
ucleotide (oligo) adaptor and the class-IIN restriction endonuclease,
XcmI. The oligo adaptor has the structure [GRAPHICS] Upon hybridizatio
n to the target DNA through the central 9-nucleotide region and with t
he addition of XcmI, the template DNA is specifically cleaved to near
completion. Hairpin structures on the template close to the hybridizat
ion site reduce the efficacy of cleavage.