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Orientation relationship

Gerard Kleywegt gerard at xray.bmc.uu.se
Tue Feb 13 11:54:59 EST 1996

In article <3120BB6E.1C7F at uabdpo.dpo.uab.edu>, Naiming Chu
<zu04117 at uabdpo.dpo.uab.edu> wrote:

?> Experts:
?> I am working on a dimer structure which has 1,2 molecules in asymmetry 
?> unit. Its space group is P21.
?> Now I am applying (-x,y+1/2,-z) onto 1,2 then get 1',2'. I expect the 
?> rotation angle between 1' and 2 should be the same as 1,2.

why is that ?  the angle 1',2' is identical to the angle 1,2

take the special case, where the dyad coincides with the b-axis
angle 1,2 = 180 degrees
apply the screw operator to get 1',2'
the angle 1',2 is zero degrees

?> Would be grateful for any comment!
?> Naiming

Gerard J. Kleywegt
Department of Molecular Biology, Biomedical Centre
Uppsala University, Uppsala, SWEDEN

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