36 time an implication of a Fe–S cluster in catalysis within the ADP-ribosyltransferase family. We here report the 1H, 15N and 13C assignments of NarE protein from N. meningitidis as a preliminary step towards characterizing its three- dimensional structure and elucidating the role of the iron– sulfur center in the catalytic mechanism. Methods and experiments The NarE gene was PCR ampliﬁed from the chromo- somal DNA of N. meningitidis MC58 strain and cloned into a pET21b? plasmid (Novagen) under the control of the T7 promoter. The resulting expression vector encodes a 17 kDa fusion protein that contains the wild-type NarE sequence (145 residues) followed by a 8-residue C-ter- minal histidine-tag (LEHHHHHH) used for puriﬁcation purposes. The pET21b? plasmid was transformed into an Escherichia coli BL21 (DE3) expression strain. Recom- binant protein was prepared from cells grown to an OD600 Fig. 1 Assigned 15N–1H HSQC spectrum of the 15N-labeled NarE protein acquired at 750 MHz and 27 C. Amide side-chain resonances are connected by solid lines L. Carlier et al. of 0.5–0.6 at 37 C in a bacterial culture supplemented by 100 lg/ml ampicillin. Protein expression was then induced by addition of 1 mM isopropyl-1-thio-b-D-galac- topyranoside (IPTG), and the culture was further grown for 3 h at 37 C. The cells were harvested by centrifuga- tion (8,0009g for 30 min), resuspended in 50 mM phos- phate buffer (pH 8.0) containing 300 mM NaCl, and lysed with a French press cell (SLM, Aminco). The soluble fraction enriched with the NarE protein was separated from the inclusion bodies by centrifugation at 39,2009g for 45 min, and loaded on a nickel afﬁnity chromatography column (GE Healthcare). The protein was puriﬁed using IMAC standard protocols and an imidazole concentration of 125 mM was required to elute recombinant NarE. A second step of puriﬁcation was performed using anion exchange QHP chromatography (GE Healthcare). Fractions containing the target protein were collected at a NaCl concentration of 300 mM and ﬁnally concentrated by ultraﬁltration using a 3-kDa cutoff membrane (Millipore). 123