A yedU gene product with a molecular mass of 31 kDa is a hypothetical protein with no known function. The protein was puri®ed and crystallized at 296 K. X-ray diffraction data have been collected to 2.3 A Ê using synchrotron radiation. The crystals belong to the primitive orthorhombic system, with unit-cell parameters a = 50.56, b = 63.45, c = 168.02 A Ê . The asymmetric unit contains two monomers of the protein, with a corresponding V M of 2.25 A Ê 3 Da À1 and a solvent content of 44.84%.