The nick translation procedure has been introduced in 1977 by Righy et al. (1). It is commonly used to label purified DNA in vitro. This technique relies on combined 5′→3′ polymerase and 5′→3′ exonuclease activities of Escherichia coli DNA polymerase I. If a nick or single strand break with a 3′ hydroxyl terminus is present in a duplex DNA molecule, the enzyme will translocate it, removing nucleotides ahead of it by 5′→3′ exonuclease activity and synthesizing the new DNA strand behind it using 5′→3′ polymerase activity (2). When labeled deoxyribonucleotides are used as substrates, the original unlabeled nucleotides in the DNA template are replaced by the labeled ones.