Abstract: A method is provided for analyzing DNA molecules having unknown 3? terminal sequences. The method involves contacting a DNA molecule with a plurality of template oligonucleotides blocked at their 3? termini such that the template oligonucleotides are not extendable by DNA polymerase. The 3? proximal portions of each of the template oligonucleotides comprise a region of random sequence and the 5? proximal portions of each of the template oligonucleotides comprise the complement of a tag sequence. The DNA molecule and the template oligonucleotides are combined under conditions wherein the 3? terminus of the DNA molecule hybridizes to the 3? proximal portion of a template oligonucleotide and is extended by a DNA polymerase to produce a DNA molecule comprising a 3? terminal tag sequence, and wherein the template oligonucleotide is not extended.