Fig. 6.

Indexing of layer lines in the Fourier transform of a helical assembly. (A) Overlay of the near-side lattice on the Fourier transform of Ca-ATPase. (B) Corresponding plot of Bessel order (n) vs. layer line height (ℓ). Assignment of (1,0) and (0,1) layer lines is arbitrary, but once chosen then all of the other visible layer lines should be either a linear combination of these two, or a consequence of mm symmetry in the transform. The radial positions of the layer lines are distorted relative to a planar 2D lattice due to the behavior of Bessel functions, which have a non-linear relationship between the radial position of their first maximum and their order, n. Nevertheless, the axial positions of the layer lines should be accurate.