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 (PubMed:9499401). Stimulates ATP hydrolysis and the folding of unfolded proteins mediated by HSPA1A/B (in vitro) (PubMed:24318877). Interacts with DNAJC3 (PubMed:9920933). 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 (PubMed:9499401). Translocates rapidly from the cytoplasm to the nucleus, and especially to the nucleoli, upon heat shock. By heat shock.