Figure 4

The missing-wedge correction on two simulated 3D maps of GroEL reconstructed from the noisy tilt series (SNR = 0.3) within the tilt angle range of ± 15° and ± 60°. (A) Two perpendicular views of the object of GroEL, (B its projection on the X-Z plane and (C) the corresponding Fourier transform. (D) The initial 3D map, shown from two perpendicular views. The initial 3D map was constructed from a noisy tilt series (SNR = 0.3) in a range of ±15° in steps of 1.5°, while the ideal 3D map was constructed from that of ±90°. (E) The projection of the initial 3D map on the X-Z plane and (F) its Fourier transform. (G) The FSC curves of the initial, ideal and iterative 3D maps against the object. The iterative 3D maps were generated after 1, 2, 10, and 100 cycles of interaction of missing-wedge correction. (H) The final restored 3D map (after 1,000 iterations of missing-wedge correction), shown from two perpendicular views, (I) the corresponding 2D projection (along the X-Z plane) and (J) the Fourier transform. (K) To reduce the influence of noise, the noisy tilt series (SNR = 0.3) were filtered to 4 Å before generating an initial 3D map for restoration. The final restored 3D map after 1,000 iterations is shown from two perpendicular views, as well as the (L) 2D projection (along the X-Z plane) and (M) Fourier transform. (N) The FSC curves of the initial, ideal and iterative 3D maps against the object. (O-Y) The procedures were repeated by using the above tilt series for the angle range of ±60°. All 3D maps were low-pass filtered to 8 Å. Scale bars: 50 nm.