Molecular chaperone that promotes the maturation; structural maintenance and proper regulation of specific target proteins involved in cell cycle control and signal transduction. Undergoes a functional cycle that is linked to its ATPase activity. The nucleotide-free form of the dimer is found in an open conformation in which the N-termini are not dimerized and the complex is ready for client protein binding. Binding of ATP induces large conformational changes; resulting in the formation of a ring-like closed structure in which the N-terminal domains associate intramolecularly with the middle domain and also dimerize with each other; stimulating their intrinsic ATPase activity and acting as a clamp on the substrate. Finally; ATP hydrolysis results in the release of the substrate. 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. Required for growth at high temperatures. {ECO:0000269|PubMed:17114002}.