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![[Figure 4]](yt5034fig4mag.jpg)
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Figure 4
The relationship between the [n1, n2] helical scheme and the helical symmetry utilized in two common indexing systems. The dots in the figure represent two properties. Firstly, they represent asymmetric units based on a simple helical structure which is described by a one-start helix (t = 4 and u = 13) with 13 subunits and four turns completing a repeat of distance c. Secondly, they describe a simplified diffraction pattern of the same helical structure. Thus, instead of showing the layer-line pattern for n-order Bessel diffraction, each dot gives the position of (n, l) diffraction where the layer-line pattern has a maximum diffraction peak at the ∼n + 2 position (Diaz et al., 2010  ). The diffraction pattern in terms of −l and n is related to the helical net description with 13 subunits enclosed by orange lines as a repeating unit. The two implicit helical symmetries, l = tn + um and n = h n10 − k n01, are then related by the [3, 1] and [3, −2] helical symmetry in (a) and (b), respectively, with n10 = n1 and n01 = n2. In the figure, each dot is labeled with an (h, k; n, l, m) index and the helical lines are in terms of the [n1, n2] helical symmetry. |
![[Figure 4]](yt5034fig4.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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