Symmetry
|
Notationa
|
Standard
Origin
|
Standard
Orientation
|
asymmetric
|
C1
|
user-defined
|
user-defined
|
cyclic
|
C<n>
|
on symmetry
axis (z-coordinate user-defined)
|
z-axis on
symmetry axis
|
dihedral
|
D<n>
|
intersection
of symmetry axes
|
z-axis on
principal symmetry axis, 2-fold on x-axis
|
tetrahedral
|
T
|
intersection
of symmetry axes |
2-fold axes
on x,y,z axes
|
| octahedralb |
O
|
intersection
of symmetry axes |
4-fold axes
on x,y,z axes
|
icosahedral,
dodecahedral
|
I
|
intersection
of symmetry axes |
2-fold axes
on x,y,z axes, front-most 5-fold vertices in yz planec,
front-most 3-fold axes in the xz planec
|
helical
|
H<rise>,<angle>,
<1/2>,<n>
|
on helical
axis, at intersection with dyad axis (if present)
|
z-axis on
helical axis, dyad axis on x (if present)
|
crystal
|
<sg>
|
phase origin
of space group
|
defined by
space group
|
a<n>: n-fold symmetry for cyclic and dihedral point
groups, as well as for helices.
<sg>: space group notation.
<1/2>: 1 = no dyad axis, 2 = dyad axis
balso the symmetry of a cube
cwith the positive z-axis pointing at the viewer and the x
and y axes perpendicular to viewer
Reference
Heymann
et al. (2005) "Common
conventions for interchange and archiving of three-dimensional electron
microscopy information in structural biology"
Journal of Structural Biology 151, 196-207; Corrigendum (2006)
153, 312.