The complete gene encoding Topoisomerase 1 (Topo I) from Mycobacterium tuberculosis (MTb), Erdman strain, has been isolated and sequenced. The coding region of this gene is 2700 nt encoding a polypeptide of 900 amino acids with a calculated molecular mass of 99353 Da. The amino-acid sequence identity compared to E. coli and Synechococcus Topo I is 22 and 30%, respectively. The gene was expressed in E. coli BL21(DE3) and purified to near homogeneity. Recombinant MTb Topo I is enzymatically active, relaxing negatively supercoiled DNA in a magnesium-dependent, ATP-independent reaction. Spermidine, a typical inhibitor of prokaryotic type I DNA topoisomerase, inhibits the activity. Unlike the more well-characterized E. coli Topo I, MTb Topo I does not contain a zinc-finger DNA-binding motif in the C-terminal domain of the protein.