Restriction endonuclease NarI cleaves DNA using a two-site mechanism, placing it in the Type IIe class of restriction endonucleases. Although these enzymes have very useful recognition sequences, the two-site mechanism limits the practical application. Site preferences often cause incomplete substrate digestion. Oligonucleotide activation of NarI eliminates incomplete digestions, making it possible to use NarI restriction sites in many common molecular biology techniques. A modified oligonucleotide was chosen for optimal activation of restriction endonuclease NarI. This oligonucleotide was demonstrated to allow complete digestion in many commonly used substrates.