A single mutation of restriction endonuclease EcoRII led to a new crystal form that diffracts to 2.1 A resolution.

R88A, a mutant of the type IIE restriction endonuclease EcoRII, has been crystallized in space group P2(1), with unit-cell parameters a = 58.7, b = 92.4, c = 88.3 A, beta = 108.1 degrees. There are two monomers in the asymmetric unit and the solvent content is estimated to be 50% by volume. The crystals diffract to 2.1 A resolution, which is much higher than that of the wild type, which diffracted to 2.8 A resolution. The mutant crystals have been used in the identification of an excellent heavy-atom derivative.