A protein capable of inhibiting the DNA gyrase activity of bacteria (DNA gyrase inhibitor protein DGI); host cells transformed by a replicable expression vector containing a DNA encoding DGI; a process for producing DGI which comprises culturing these host cells; a method for identifying medicinal compounds which comprises assaying the effect of altering the DNA gyrase inhibitory activity of DGI; and a method for identifying medicinal compounds characterized by assaying the effect of altering the expression of the gene encoding DGI.
