The crystal structure of the urease gamma subunit (UreA) from Mycobacterium tuberculosis, Rv1848, has been determined at 1.8 A resolution. The asymmetric unit contains three copies of Rv1848 arranged into a homotrimer that is similar to the UreA trimer in the structure of urease from Klebsiella aerogenes. Small-angle X-ray scattering experiments indicate that the Rv1848 protein also forms trimers in solution. The observed homotrimer and the organization of urease genes within the M. tuberculosis genome suggest that M. tuberculosis urease has the (alphabetagamma)(3) composition observed for other bacterial ureases. The gamma subunit may be of primary importance for the formation of the urease quaternary structure.