The reactions of SacI, PvuII and EcoRI endonucleases

A new approach to the mechanism study of DNA restriction is suggested. It is based on enzymatic hydrolysis of DNA in the presence of organic solvent. We found that in the presence of DMSO (10% v/v), the superhelical cleavage of pBR322 DNA by restriction endonucleases SacI and EcoRI proceeds with extensive accumulation of an intermediate, the single-nicked circular DNA, while with PvuII endonuclease the superhelical form is converted directly to the linear form.