Co-chaperone that binds to the molecular chaperones Hsp90 (HSC82 and HSP82) and Hsp70 (SSA1). Stimulates SSA1 ATPase activity, but not Hsp90 ATPase activity. Involved in only a subset of Hsp90 functions. Monomer. Component of Hsp70 and Hsp90 chaperone complexes. Interacts (via TPR repeats) with HSC82 and HSP82 (via C-terminal MEEVD pentapeptide). Interacts with CPR7, SSA1 and SPI1. Not induced by heat shock. Present with 672 molecules/cell in log phase SD medium. Belongs to the TTC4 family.