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. In response to cellular stress, up-regulated in distal tissues in a pqm-1-dependent manner, preventing protein misfolding and maintaining proteostasis (PubMed:29949773). 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 (PubMed:10790386, PubMed:7828815). 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 (PubMed:16466390). Regulates yap-1 nuclear export after heat shock treatment (PubMed:23396260). Homodimer (PubMed:26593036). Interacts (via TPR repeat-binding and central region) with pph-5 (via phosphatase domain); the interaction promotes pph-5 phosphatase activity (PubMed:26593036). Interacts (via central region) with co-chaperone cdc-37 (via N-terminus); the interaction inhibits daf-21 ATPase activity (PubMed:23569206). Perinuclear region of somatic cells. In the embryo comma stage, expression is strongly detected in cells of the head region and less so in other areas. In early larvae, expressed in postembryonic germ cells derived from Z2 and Z3 cells and the head region, in both hermaphrodites and males. Under heat stress conditions, larval expression is not only detected in germ cells, but also all over the body. In adult hermaphrodites, expression is localized uniquely in the germ cells. Highly expressed throughout development. Induced by heat-stress. The TPR repeat-binding motif mediates interaction with TPR repeat-containing proteins. Belongs to the heat shock protein 90 family.