Functions as co-chaperone for HSPA1B and negatively regulates the translocation of BAX from the cytosol to mitochondria in response to cellular stress, thereby protecting cells against apoptosis. Promotes apoptosis in response to cellular stress mediated by exposure to anisomycin or UV. Stimulates ATP hydrolysis, but not the folding of unfolded proteins mediated by HSPA1A (in vitro) (By similarity). Co-chaperone for HSPA8/Hsc70. Plays a role in protein transport into mitochondria via its role as co-chaperone (PubMed:10816573). Identified in a complex with HSPA1B and BAX. Interacts with RNF207. Primarily cytoplasmic and associated with microsomes. A minor proportion is associated with nuclei and mitochondria. Detected in liver (at protein level).