Extent of 7-fold symmetry of class averages of single-ring GroEL particles containing the Phe-44 → Trp single mutation or the Phe-44 → Trp, Asp-155 → Ala double mutation in the presence of different concentrations of ATP. Each class average was rotated by N (an integer that runs from 1 to 360) × 1°. The extent of the 7-fold symmetry of the different class averages was determined by calculating a cross-correlation coefficient, r, between the nonrotated class average and the rotated ones by using procedures written with spider (27). The respective rotational correlation plots for the Phe-44 → Trp single mutant and the Phe-44 → Trp, Asp-155 → Ala double mutant, in the absence of ATP, are shown in A and B. The respective rotational correlation plots for Phe-44 → Trp single mutant and the Phe-44 → Trp, Asp-155 → Ala double mutant, in the presence of 100 μM ATP, are shown in C and D. The respective rotational correlation plots for the Phe-44 → Trp single mutant and the Phe-44 → Trp, Asp-155 → Ala double mutant, in the presence of 5 μM ATP, are shown in E and F.