Sedimentation profiles of heat-treated 70S ribosomes prepared from dnaK+ (MC41.14) and ΔdnaK (BB11) strains. (A,B) Ribosomes from wild-type and mutant strains, respectively, were incubated at various temperatures (0°C, 30°C, 40°C, or 50°C) and then subjected to sucrose-gradient centrifugations. The profiles were practically identical; here those after a 50°C incubation are shown. (C,D) Same as A and B, respectively, but incubation temperature was 60°C; (E,F) same as A and B, respectively, but incubation temperature was 70°C. For details, see Materials and Methods.