Abstract
Replacement of the α4 helix of ParC with that of GyrA increased the stability of topoisomerase IV-quinolone-DNA ternary complexes. This mutant topoisomerase IV-mediated cell killing was more efficient than topoisomerase IV-mediated cell killing in Escherichia coli . Thus, the α4 helix plays critical roles in determining the stability and the cytotoxicity of ternary complexes.