Many proteins in bacterial cells fold in the chaperonin cage made of the central cavity of GroEL capped by GroES. Recent studies indicate that the polypeptide in the cage spends the most time as a state tethered dynamically to the GroEL/GroES interface region, in which folding occurs in the polypeptide segments away from the tethered site (F. Motojima & M. Yoshida, EMBO J. (2010) 29,4008-4019). In support of this, we show here that a polypeptide in the cage tethered covalently to an appropriate site in the GroEL/GroES interface region can fold to a near-native structure. (C) 2015 Elsevier Inc. All rights reserved.