ABSTRACT
Recently, it was revealed that restriction endonucleases widely used in genetic engineering and molecular biology are diverse not only in DNA sequence specificities but also in mechanisms of their interaction with DNA. In the review type IIE and IIF restriction endonucleases which require the simultaneous interaction with two copies of their recognition sequence for effective hydrolysis of DNA are considered. Crystal structures of these enzymes and their complexes with DNA as well as stepwise interaction with DNA, mechanisms of catalysis and enzyme-mediated DNA looping are discussed. A novel type of DNA-protein recognition was found for type IIE endonucleases when two copies of the same DNA sequence specifically interact with two different amino acid sequences and two structural motifs located in one polypeptide chain.