X-ray crystallographic characterization and phasing of an NtrC homologue

The ZraR (HydG) protein is a 441-amino-acid protein with three functional domains and is homologous to the general nitrogen-regulatory protein NtrC that regulates nitrogen assimilation in many bacteria. The AAA and DNA-binding domains (residues 141-441) of the ZraR protein from Salmonella typhimurium were crystallized using the sitting-drop vapour-diffusion method. X-ray diffraction data from the native crystal have been collected to 3.0 A resolution. Initial phasing was successfully performed by the SIRAS method using derivativatized crystals soaked in 1 mM ethylmercuric phosphate. Preliminary structural analysis shows the presence of a hexamer in the asymmetric unit. Model building is in progress.