Molecular chaperone that assists in the folding or refolding of nascent or denatured proteins along with ATP hydrolysis (Probable). ATPase activity is highest in thermosome assemblies containing CCT1:CCT2, followed by assemblies containing CCT1:CCT2:CCT3. Required for thermosome ATPase activity. Not required for growth. The thermosome or CCT complex is a oligomeric complex of two octameric double-ring structures; the complex is probably a heterooligomer of CCT1, CCT2 AND CCT3 with yet unknown stoichiometry. By heat shock (at protein level). Can substitute for loss of cct2 or cct3. One of either cct1 or cct2 is required for growth. Belongs to the TCP-1 chaperonin family.