Oligonucleotide duplexes containing CC(A/T)GG stimulate cleavage of refractory DNA by restriction endonuclease EcoRII

Some DNA species are resistant towards the restriction endonuclease EcoRII despite the presence of unmodified recognition sites. We show that 14 base-pair oligonucleotide duplexes containing the EcoRII recognition site 5'-CC(A/T)GG are cleaved by this enzyme and are able to stimulate EcoRII cleavage of such resistant DNA molecules (e.g. DNA of bacterial virus T3). A direct correlation between the concentration of oligonucleotide duplex molecules and the degree of EcoRII digestion of the primarily resistant DNA is observed. This indicates a stoichiometric rather than a catalytic mode of enzyme activation. An excess of DNA devoid of EcoRII sites ('non-site' DNA, e.g. MvaI-digested T7 DNA) does not interfere with the activity of EcoRII.