Purification and some properties of an inhibitor for a yeast pleiotropic drug resistant pump from Kitasatospora sp E-420

A strain producing an inhibitor for pleiotropic drug resistant 5 (Pdr5) was isolated using our original screening system in yeast. The strain was clas sified and named as Kitasatospora sp. E-420. The purified inhibitor (molecu lar weight = 1,193 by FAB-MS) inhibited a Pdr5-mediated efflux of cyclohexi mide and cerulenin. The intracellular accumulation of a fluorescent dye, rh odamine 123, by the inhibitor was also confirmed. Some physicochemical data suggested that the Pdr5-specific inhibitor was different from an immunosup pressant, FK506, reported as the only inhibitor of Pdr5 in vivo.