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BglII is a type-II restriction endonuclease (RE) that recognizes and cleaves the DNA sequence AGACTC. The crystal structure of BglII bound to DNA resembles other REs, with a major α/β core domain containing a central β sheet flanked by α helices. In the February Nature Structural Biology, Lukacs et al. describe the structure of the free BglII enzyme, which provides an understanding of how DNA enters the binding cleft for hydrolysis (Nat Struct Biol 2001, 8:126-130). It seems, from the free-enzyme structure, that an unusual scissor-like motion allows the entry of DNA. The individual monomers swing out by as much as 50°, like scissor blades, producing significant effects on the tertiary and quaternary structure. The free-BglII structure offers a new model for understanding protein-DNA recognition events.

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