Interacts with HSP70 and can stimulate its ATPase activity. Stimulates the association between HSC70 and HIP. Negatively regulates heat shock-induced HSF1 transcriptional activity during the attenuation and recovery phase period of the heat shock response. Stimulates ATP hydrolysis and the folding of unfolded proteins mediated by HSPA1A/B (in vitro). Interacts with DNAJC3. Interacts with HSF1 (via transactivation domain); this interaction results in the inhibition of heat shock- and HSF1-induced transcriptional activity during the attenuation and recovery phase period of the heat shock response. Translocates rapidly from the cytoplasm to the nucleus, and especially to the nucleoli, upon heat shock. By heat shock.