CRYSTAL-STRUCTURE OF RESTRICTION-ENDONUCLEASE BG I BOUND TO ITS INTERRUPTED DNA RECOGNITION SEQUENCE/

The crystal structure of the type II restriction endonuclease BglI bou nd to DNA containing its specific recognition sequence has been determ ined at 2.2 Angstrom resolution, This is the first structure of a rest riction endonuclease that recognizes and cleaves an interrupted DNA se quence, producing 3' overhanging ends. BglI is a homodimer that binds its specific DNA sequence with the minor groove facing the protein, Pa rts of the enzyme reach into both the major and minor grooves to conta ct the edges of the bases within the recognition half-sites. The arran gement of active site residues is strikingly similar to other restrict ion endonucleases, but the coordination of two calcium ions at the act ive site gives new insight into the catalytic mechanism. Surprisingly, the core of a BglI subunit displays a striking similarity to subunits of EcoRV and PvuII, but the dimer structure is dramatically different . The BglI-DNA complex demonstrates, for the first time, that a conser ved subunit fold can dimerize in more than one way, resulting in diffe rent DNA cleavage patterns.