Co-chaperone for HSP70 and HSC70 chaperone proteins. Acts as a nucleotide-exchange factor (NEF) promoting the release of ADP from the HSP70 and HSC70 proteins thereby triggering client/substrate protein release (PubMed:24318877, PubMed:9873016). Binds to the ATPase domain of HSP/HSC70 chaperones (PubMed:9873016). May interact with NWD1 (PubMed:24681825). Interacts with HSPA1A (via NBD), HSPA1B (via NBD) and HSPA8 (PubMed:24318877). May interact with DNJC9; the interaction seems to be histone-dependent (PubMed:33857403).