A purified BamHI-cut DNA fragment is end-labeled (i.e. only the terminal 5' phosphate from each strand is labelled) and partially digested with the enzyme DpnI. The reaction conditions were such that each DNA molecule, if cut at all, is cut only once. The resulting DNA fragments were electrophoresed on an agarose gel, autoradiographed and the longest fragment that was shorter than the uncut, original DNA was isolated and again partially digested with DPnI. Both reaction mixtures were electrophoresed on an agarose gel and the fragments visualized by autoradiography.
Original partial digestion with DpnI: 2300, 2250, 1950, 1750, 1450, 850, 550, 350, 50 bp. Second partial DpnI digestion: 2250, 1750, 850, 350 bp.
Provide a physical map of the DpnI restriction sites of the original DNA.