Molecular chaperone that promotes the maturation, structural maintenance and proper regulation of specific target proteins involved for instance in cell cycle control and signal transduction. Undergoes a functional cycle that is linked to its ATPase activity. This cycle probably induces conformational changes in the client proteins, thereby causing their activation. Interacts dynamically with various co-chaperones that modulate its substrate recognition, ATPase cycle and chaperone function. By stabilizing the receptor-type guanylate cyclase daf-11 or another signal transduction component that regulates cGMP levels, plays a role in dauer formation and chemotaxis to non-volatile and volatile attractants detected by AWC sensory neurons. Participates in the control of cell cycle progression at the prophase/metaphase transition in oocyte development by ensuring the activity of wee-1.3 kinase, which negatively regulates cdk-1 through its phosphorylation. Regulates yap-1 nuclear export after heat shock treatment. Homodimer. Interacts (via TPR repeat-binding and central region) with pph-5 (via phosphatase domain); the interaction promotes pph-5 phosphatase activity. Interacts (via central region) with co-chaperone cdc-37 (via N-terminus); the interaction inhibits daf-21 ATPase activity. Perinuclear region of somatic cells. The TPR repeat-binding motif mediates interaction with TPR repeat-containing proteins. Belongs to the heat shock protein 90 family.