TRAP1 requires the mitochondrial Hsp70 system for protein folding. Averages of three independent measurements ± SD are shown. (A) Reactivation of heat-denatured FFL after 120 min by hHsp90, hTRAP1, or bHsp90 together with RRL or the bacterial Hsp70 system (KJE). Recovered FFL activities are expressed relative to native FFL. (B) Reactivation of heat-denatured FFL without hTRAP1 (no TRAP1), with hTRAP1 (TRAP1), or with hTRAP1 and 5 mM ATP (TRAP1-ATP), and together with Mortalin/Mdj1/Mge1. FFL recovery was monitored every 20 min for 120 min.