Fig. 7. Projection structure of SecYEG. Projection maps calculated from merged amplitudes and phases from 12 independent lattices of crystals embedded in trehalose. (A) Map drawn to 9 Å in P1 (no symmetry imposed). (B) With P12₁ symmetry imposed. An isotropic temperature factor of –600 Å² was applied in (A) and (B) to compensate partially for the resolution-dependent degradation of image-derived amplitudes (Unger et al., 1997a). (C) Map at 9 Å resolution with imposed P12₁ symmetry without temperature factor adjustments. (D) Map at 15 Å resolution with P12₁ symmetry imposed. In all cases, four unit cells are shown, and one unit cell (containing two symmetry-related asymmetric units) is boxed. The solid lines indicate densities above the mean. Scale bar, 20 Å.