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![[Figure 7]](yt5034fig7mag.jpg)
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Figure 7
The procedure of serial density-map superimpositions illustrates the determination of the 1-D helical symmetry from a helical EM structure. The bateriophage fd coat protein (EMD-1240) is used here for demonstration. The original EM structure is displayed as a yellow isosurface and the symmetry-transformed density map is shown as a red isosurface. A first superimposition, denoted by the 1-D helical symmetry operation [1, 0, 0.0, 34.8], gives the result of a 34.8 Å translation only. Following an additional rotation of 2.6° denoted by [1, 0, 2.6, 34.8], the outcome of perfect superposition determines the [φ, δ] of 1-D helical symmetry for the set of ten-start primary protofilaments. Applying a tenfold rotation [10, 0, 2.6, 34.8] then gives the third superimposition. Finally, an extra translation defined by n2 = 5 completes the determination of 1-D helical symmetry [10, 5, 2.6, 34.8] for the EMD-1240 structure. |
![[Figure 7]](yt5034fig7.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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