CRYSTALLIZATION AND PRELIMINARY-X-RAY ANALYSIS OF RESTRICTION-ENDONUCLEASE FOKI BOUND TO DNA

FokI is a type Ils restriction endonuclease which recognizes an asymme tric DNA sequence and cleaves DNA a short distance away from the seque nce, The enzyme is bipartite in nature with its DNA recognition and cl eavage functions located on distinct domains, We report here cocrystal s of the complete FokI enzyme (579 amino acids) hound to a 20-bp DNA f ragment containing its recognition sequence, The complex is amongst th e largest protein-DNA complexes to he crystallized, and required macro seeding techniques for optimal crystal growth, The cocrystals diffract to at least 2.8 Angstrom in resolution and belong to space group P2(1 ) with unit cell dimensions of a = 67.9 Angstrom, b = 119.8 Angstrom, c = 69.1 Angstrom, beta = 96.6 degrees. Using specific amino acid anal ysis we show that asymmetric unit contains a single FokI molecule boun d to the 20-bp DNA fragment, This paper reports the first cocrystals o f a type IIs restriction endonuclease. (C) 1997 Federation of European Biochemical Societies.