Bacillus subtilis Bs gyrA and gyrB genes specifying the DNA gyrase subunits, and parC and parE genes specifying the DNA topoisomerase IV subunits, have been separately cloned and expressed in Escherichia coli as hexahistidine (his6)-tagged recombinant proteins. Purification of the gyrA and gyrB subunits together resulted in predominantly two bands at molecular weights of 94 and 73 kDa; purification of the parC and parE subunits together resulted in predominantly two bands at molecular weights of 93 and 75 kDa, as predicted by their respective sequences. The ability of the subunits to complement their partner was tested in an ATP-dependent decatenation/supercoiling assay system. The results demonstrated that the DNA gyrase and the topoisomerase IV subunits produce the expected supercoiled DNA and relaxed DNA products, respectively. Additionally, inhibition of these two enzymes by fluoroquinolones has been shown to be comparable to those of the DNA gyrases and topoisomerases of other bacterial strains. In sum, the biological and enzymatic properties of these products are consistent with their authenticity as DNA gyrase and DNA topoisomerase IV enzymes from B. subtilis. (C) 2003 Elsevier Science (USA). All rights reserved.