Yeast tRNA-thiouridine modification protein 1 (Tum1p), a crucial component of the Urm1 system, is believed to play important roles in protein urmylation and tRNA-thiouridine modification. Previous studies have demonstrated that the con-served residue Cys259 in the C-terminal rhodanese-like domain of Tum1p is essential for these sulfur-transfer activities. Here, recombinant Tum1p protein has been cloned and overexpressed in Escherichia coli strain BL21 (DE3). After purification, crystals of Tum1p were obtained by the hanging-drop vapour-diffusion method and diffracted to 1.9 Å resolution. The preliminary X-ray data showed that the tetragonal Tum1p crystal belonged to space group I4 1, with unit-cell parameters a = b = 120.94, c = 48.35 Å. The asymmetric unit of the crystal was assumed to contain one protein molecule, giving a Matthews coefficient of 2.41 Å 3 Da -1 and a solvent content of 49.0%. © 2011 International Union of Crystallography All rights reserved.