[phenixbb] Twinned data with Phaser

Randy John Read rjr27 at cam.ac.uk
Tue May 25 01:12:34 PDT 2021

Hi Len,

We’ve thought about accounting for twinning during MR in Phaser, but our experience is that it just reduces the signal-to-noise ratio so that you need a somewhat better model or slightly higher resolution than you would need with untwinned data.  So there always seems to be something more important to address!  

If you have a good model it should just work; if you have perfect merohedral twinning then you will probably get two solutions related by the twinning operator with similar scores, but if the twinning is partial you might only get a single solution corresponding to the major twin component.  

Best wishes,


> On 24 May 2021, at 22:45, Thomas, Leonard M. <lmthomas at ou.edu> wrote:
> Hello,
> I have been working on a structure for a very long while.  We have a number of data sets with the good ones mostly around the 3.1-3.2 A range.  I do have a determination of the structure but would like to see if I can get the structure determined with a slightly higher resolution data set at around 2.7 A.  Problem is the 2.7 data is twinned.  Are there settings in Phaser to handle twinned data or is the twinning only handled during refinement?  
> Thank you for any advice, outside of forgetting about the twinned data.  
> Len 
> Leonard Thomas, Ph.D.
> Macromolecular Crystallography Laboratory
> Oklahoma COBRE in Structural Biology
> Price Family Foundation Institute of Structural Biology
> University of Oklahoma
> Department of Chemistry and Biochemistry
> Stephenson Life Sciences Research Center
> 101 Stephenson Parkway
> Norman, OK 73019-5251
> Office: (405)325-1126
> lmthomas at ou.edu
> http://www.ou.edu/structuralbiology/cobre-core-facilities/mcl
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Randy J. Read
Department of Haematology, University of Cambridge
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