Here, we report the three-dimensional structure of severe acute respiratory syndrome coronavirus (SARS-CoV) nsP7, a component of the SARS-CoV replicase polyprotein. The coronavirus replicase carries out regulatory tasks involved in the maintenance, transcription, and replication of the coronavirus genome. nsP7 was found to assume a compact architecture in solution, which is comprised primarily of helical secondary structures. Three helices (alpha2 to alpha4) form a flat up-down-up antiparallel alpha-helix sheet. The N-terminal segment of residues 1 to 22, containing two turns of alpha-helix and one turn of 3(10)-helix, is packed across the surface of alpha2 and alpha3 in the helix sheet, with the alpha-helical region oriented at a 60 degrees angle relative to alpha2 and alpha3. The surface charge distribution is pronouncedly asymmetrical, with the flat surface of the helical sheet showing a large negatively charged region adjacent to a large hydrophobic patch and the opposite side containing a positively charged groove that extends along the helix alpha1. Each of these three areas is thus implicated as a potential site for protein-protein interactions.