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. Author manuscript; available in PMC: 2013 Jan 10.
Published in final edited form as: Nat Struct Mol Biol. 2007 Sep 16;14(10):921–926. doi: 10.1038/nsmb1300

Figure 2.

Figure 2

Variable twist, and overcoming it with the IHRSR approach. (a) Histogram of average twists for segments of frozen-hydrated ParM filaments. (b) The convergence of the IHRSR procedure is shown for cryo-EM segments of ParM classified as having a mean twist of ~162.5°. A solid featureless object (cylinder, left) was used as an initial reference. The IHRSR procedure was run twice, starting the search at either 162.0° (●) or 165.0° (■). After ~50 cycles, the two different sets converged to the same symmetry and the same reconstructed volume. An unsymmetrized volume from the seventieth cycle is shown as gray density at right. Each cycle, such a volume is analyzed to determine the symmetry within it, and this symmetry is imposed on the volume to generate a new symmetrized reference for the next cycle. The unsymmetrized volume shown has not been corrected for the CTF.