A thermostable ribonuclease HIII from Bacillus stearothermophilus (Bst RNase HIII) was crystallized and preliminary crystallographic studies were performed. Plate-like overlapping polycrystals were grown by the sitting-drop vapour-diffusion method at 283 K. Native X-ray diffraction data were collected to 2.8 A resolution using synchrotron radiation from station BL44XU at SPring-8. The crystals belong to the orthorhombic space group P2(1)2(1)2, with unit-cell parameters a = 66.73, b = 108.62, c = 48.29 A. Assuming one molecule per asymmetric unit, the VM value was 2.59 A3 Da(-1) and the solvent content was 52.2%.
