[phenixbb] NCS Restraints

Vellieux Frederic Frederic.Vellieux at ibs.fr
Fri Jul 1 06:00:50 PDT 2011

Yuri wrote:
> Hi Pavel,
>> It's rather packing.. Say, if more than one copy packs in the asymmetric
>> unit then you have NCS, roughly speaking..
> So is it correct to say that in cases where you have 1 molecule per 
> ASU, there will be no NCS only crystallographic symmetry??

In the case where you have 1 molecule per asymmetric unit, you have 
1-fold non-crystallographic redundancy and this is why "solvent 
flattening" can be powerful (try to derive the "molecular replacement 
equation" yourself, and you'll understand that there is still some 
redundancy of information for "1-fold non crystallographic symmetry" 
when there is a large enough fraction of solvent in the unit cell..., 
same equation except that there is no summation over N 
non-crystallographic equivalents)

>> In other words, if for the same enzyme one crystal goes to 3.1 and
>> another 1.5 A could one have significant NCS but not the other?
>> I'm not sure I understood this... May some one else did?
> I was trying to understand if this phenomenon would be noticeable 
> depending on the resolution only...
> You and Nathaniel pretty much answered this now...

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