Crystallization and preliminary X-ray diffraction studies of NusG, a protein shared by the transcription and translation machines

N‐utilization factor G (NusG) from Aquifex aeolicus (Aa) was overexpressed in Escherichia coli, purified and crystallized using the hanging‐drop vapor‐diffusion technique. The drops consisted of 2.5 µl protein solution (∼30 mg ml−1 in 20 mM Tris–HCl pH 8.0, 200 mM NaCl, 2 mM EDTA and 10 mM DTT) and 2.5 µl reservoir solution (0.085 M Na HEPES pH 7.5, 15% glycerol, 11% 2‐propanol and 20% PEG 4000) derived from condition number 41 of the Hampton Cryo Screen. The crystals grew at 291 ± 1 K and reached dimensions of 0.2 × 0.1 × 0.05 mm in 5–7 d. The crystals, which diffracted to 2.45 Å resolution, belonged to space group C2221, with unit‐cell parameters a = 65.95, b = 124.58, c = 83.60 Å. One AaNusG molecule is present in the asymmetric unit, corresponding to a solvent content of 59.80% (Matthews coefficient = 3.06 Å3 Da−1). Crystal structure determination is in progress.