The characterization of Hsp90 from the fission yeast Schizosaccharomyces pombe was performed. Hsp90 of S. pombe existed as a dimer and exhibited ATP-dependent conformational changes. It captured unfolded proteins in the ATP-free open conformation and protected them from thermal aggregation. Hsp90 of S. pombe was also able to refold thermally denatured firefly luciferase. The co-chaperones Stil and Aha1 bound Hsp90 and modulated its activity. Because the affinity of Stil was higher than that of Aha1, the effect of Stil appeared to dominate when both co-chaperones existed simultaneously. (C) 2013, The Society for Biotechnology, Japan. All rights reserved.