I think this is called "P21", with the additional annoyance that you
need to pick your Rfree set in P212121 and then symmetry-expand it.
Otherwise, your NCS operators will constrain your "free" reflections
to have the same intensity as their "NCS mates". I'm sure you didn't
make that mistake, but a lot of other people have.
I suppose you could still call this "NCS", for "nearly
crystallographic symmetry". But I think the general term
"pseudosymmetry" is what I would use in a paper.
I have seen one case (1FYK) where the protein followed the cannonical
crystallographic symmetry and the DNA was disordered along the screw
of the double helix. Since O.L. was having a hard time interpreting
the DNA density, he re-grew the crystals with a new oligo containing a
single iodinated base to try and clear up the register, only to find
that the iodine difference map lit up _every_ base in the DNA ladder,
forming a beautiful double helix, with one atom! That is: all the
"base pairs" in the density was actually composed of an equal portion
of all the bases in the oligo.
Not exactly the situation you are in, but definitely a case where one
part of the ASU had different "symmetry" than another.
-James Holton
MAD Scientist
On Mon, Oct 10, 2011 at 2:41 PM, Jon Schuermann <[log in to unmask]> wrote:
> I am sure this has happened many many times before but I cannot find a
> reference. I have a protein/DNA complex structure where the protein has
> P212121 symmetry, but the DNA only has P21 symmetry. I know its
> pseudosymmetry caused by the NCS. Has anyone seen this with protein/DNA or
> have a reference I can add to my paper?
>
> Thanks so much,
> Jon
>
> --
> Jonathan P. Schuermann, Ph. D.
> Beamline Scientist
> NE-CAT, Building 436E
> Advanced Photon Source (APS)
> Argonne National Laboratory
> 9700 South Cass Avenue
> Argonne, IL 60439
>
> email: [log in to unmask]
> Tel: (630) 252-0682
> Fax: (630) 252-0687
>
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