You dont say what the translation vector is, or the spacegroup, but if
one of the translation components is fractional, eg 0.5 with an
orthogonal SG or 0.333 in a trigonal, then it can generate aparent
absences along an axis, and it s easy to mis-assign the spacegroup; eg
call something P212121 when in fact it is P21 2 21 or some such..
The effect of that is just what you describe..
Eleanor
Marina Siponen wrote:
> Dear CCP4 bulletin boarders,
>
> I've been experiencing problems with the refinement of a structure at a
> resolution of 1.9 Å with a ~30% pseudo-translation.
>
> The structure in question is a dimer of dimers (i.e. tetramer.) This is
> what is observed in the asu and is correct based on biological
> information. During refinement one of the two dimers refines nicely
> while the second is seeing its B-factors rise considerably > 70 or 80,
> consequently maps are degrading while R-factors are steadily decreasing.
>
> Any explanation/suggestions/experience dealing with pseudo-translation
> in data processing/solving and refinement would be particularly helpful.
> Any good literature dealing with the subject would also be greatly
> appreciated.
>
> Thank you
> Marina
>
> Marina Siponen, PhD
> Karolinska Institutet
> MBB/SGC
> Scheeles väg 2
> 171 77 Stockholm
> Sweden
> Phone: +46-8-524 868 42
> Fax: +46-8-524 868 68
> [log in to unmask]
>
>
>
>
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