A model of EcoRII restriction endonuclease action: The active complex is most likely formed by one protein subunit and one DNA recognition site

To elucidate the mechanism of interaction of restriction endonuclease EcoRI I with DNA, we studied by native gel electrophoresis the binding of this en donuclease to a set of synthetic DNA-duplexes containing the modified or ca nonical recognition sequence 5'-d(CCA/TGG)-3', All binding substrate or sub strate analogues tested could be divided into two major groups: (i) duplexe s that, at the interaction with endonuclease EcoRII, form two types of stab le complexes on native gel in the absence of Mg2+ cofactor; (ii) duplexes t hat form only one type of complex, observed both in the presence and absenc e of Mg2+, Unlike the latter, duplexes under the first group can be hydroly zed by endonuclease, Data obtained suggest that the active complex is most likely formed by one protein subunit and one DNA recognition sequence. A mo del of EcoRII endonuclease action is presented.