Binds specifically to cytosolic chaperonin (c-CPN) and transfers target proteins to it. Binds to nascent polypeptide chain and promotes folding in an environment in which there are many competing pathways for nonnative proteins. Has a role in gonadogenesis (By similarity). Heterohexamer of two PFD-alpha type and four PFD-beta type subunits. Belongs to the prefoldin subunit beta family.