Crystallization and preliminary crystallographic studies of type 1 RNase H from the hyperthermophilic archaeon Sulfolobus tokodaii 7 were performed. A crystal was grown at 277 K by the sitting-drop vapour-diffusion method. Native X-ray diffraction data were collected to 1.5 angstrom resolution using synchrotron radiation from station BL41XU at SPring-8. The crystal belongs to space group P4(3), with unit-cell parameters a = b = 39.21, c = 91.15 A. Assuming the presence of one molecule in the asymmetric unit, the Matthews coefficient V-M was calculated to be 2.1 angstrom(3) Da(-1) and the solvent content was 40.5%. The structure of a selenomethionine Sto-RNase HI mutant obtained using a MAD data set is currently being analysed.
