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. Author manuscript; available in PMC: 2014 Jun 2.
Published in final edited form as: J Struct Biol. 2006 Jun 14;157(1):106–116. doi: 10.1016/j.jsb.2006.05.012

Figure 1.

Figure 1

Overview of the IHRSR cycle. 1) A series of 2D projections are calculated from a 3D reference model. 2) Tubular crystal segments (i.e. “single-particle” subimages) are aligned against the reference projections (i.e. multi-reference alignment). 3) Single-particle subimages are back-projected to form an initial asymmetric 3D volume. 4) A helical search is conducted on the asymmetric 3D volume to determine helical symmetry parameters. 5) Helical symmetry is imposed onto the 3D volume. 1) The helically symmetric 3D volume is then used as the new “reference” model for the next round, and the cycle is iterated until a stable reconstruction is obtained. Significant modifications to the original algorithm are italicized in brackets and are described in Table 1.