Chaperones of Thermus thermophilus cooperate in reactivation of heat-inactivated proteins. The protein, inactivated at a high temperature in a TDnaKJ-GrpE set, recovered its activity during subsequent incubation with TClpB at moderate temperature (Motohashi, K., Watanabe, Y., Yohda, M., and Yoshida, M. (1999) Proc. Natl. Acad. Sci. U. S. A. 96, 7184-7189). Here, we report that the addition of chaperonin (Tcpn) at moderate temperature improves the yield of the TDnaKJ-GrpE-ClpB-dependent reactivation. The trap-Tcpn, which binds substrate protein but does not release it, inhibits reactivation severely. Maximum recovery is gained at sub-stoichiometric amounts of each component of TDnaKJ, TGrpE, and TClpB relative to the substrate monomer. These observations indicate that, driven by ATP hydrolysis, TDnaKJ-GrpE-ClpB chaperones catalytically cooperate and release heat-inactivated protein as a non-native, chaperonin-recognizable folding intermediate.