Required, in concert with Hsp40 and Hsp70 and small Hsps, for the dissociation, resolubilization and refolding of aggregates of damaged proteins after heat or other environmental stresses. Extracts proteins from aggregates by unfolding and threading them in an ATP-dependent process through the axial channel of the protein hexamer, after which they can be refolded by components of the Hsp70/Hsp40 chaperone system (By similarity). Homohexamer, forming a ring with a central pore. More concentrated in polyribosomes than in monoribosomes, and preferentially localized in the large subunit. Has 2 AAA ATPase type nucleotide-binding domains (NBDs) per monomer. ATP binding to NBD1 triggers binding of polypeptides and stimulates ATP hydrolysis at NBD2. Nucleotide binding to NBD2 is crucial for oligomerization (By similarity). The C-terminal extension is involved in oligomerization. Belongs to the ClpA/ClpB family.