Crystallization of the DNA-binding Escherichia coli protein FIS

The specific DNA-binding protein FIS (factor for inversion stimulation), which stimulates site-specific DNA inversion by interaction with an enhancer sequence, was purified from an Escherichia coli strain overproducing the protein. FIS was crystallized at room temperature by microdialysis against 1.2 to 1.5 M-sodium/potassium phosphate containing 10 mM-Tris.HCl, 0.5 to 1 M-NaCl and 1 mM-NaN3 at pH 8.0 to 8.2. The crystals are stout prisms and suitable for X-ray diffraction study beyond 2.5 A resolution. They belong to the orthorhombic space group P2(1)2(1)2(1). The unit cell has dimensions a = 47.57(4) A, b = 51.13(4) A, c = 79.83(6) A and contains one FIS dimer in the asymmetric unit.