Purification, crystallization and preliminary X‐ray analysis of the catalytic domain of the Escherichia coli tRNase colicin D

The tRNase domain of colicin D, which cleaves only tRNA Arg s at the 3′ side of their anticodon loops, has been expressed in Escherichia coli with its inhibitor protein and purified to a form free from the inhibitor using a low‐pH buffer. Crystals were obtained by the hanging‐drop vapour‐diffusion method at 278 K from a buffer containing 100 m M Tris–HCl pH 8.5, 22% PEG MME 2000 and 1 m M nickel(II) chloride. Diffraction data to 1.05 Å resolution were collected at BL41XU, SPring‐8. The crystals belong to space group P 2 1 2 1 2 1 , with unit‐cell parameters a = 34.7, b = 65.5, c = 96.5 Å.