[phenixbb] poor phasing

Francis E Reyes Francis.Reyes at Colorado.EDU
Mon Apr 27 05:48:15 PDT 2009

I had a case of P 41 21 2 at 2.5A that had a perfect SAD map for  
iodine soaked data. However, the R statistics were stuck in the mid  
30's with over 2/3 of the asymmetric unit built (the other 1/3 at the  
N/C termini and internal loop region remained disordered). Though it  
didn't test positive for twinning, I considered perfect twinning and  
scaled it to P41 with now two molecules per asu. A few (maybe 2-3)  
residues could be built at the N/C termini and the statistics dropped  
into the mid 20's  with NCS (due to lower symmetry).

I have yet to find a twinning test that can assess perfect twinning.  
So you might want to consider it.


On Apr 27, 2009, at 6:30 AM, vennila Natesan wrote:

> Dear Tom
> Thankyou for your kind reply.I checked my data witn phenix.xtriage
> and there are good anomalous signal (>0.05)in all the resolution  
> shells.
> Also the systematic absences show it is P43212.Still i couldnt
> solve using phenix.Where is the thing going wrong?
> Xtriage results also showed no twinning.
> My previous message:
> I am using phenix1.4-4 version. In autosol, got the score of 10.24  
> for one iodine soaked data.
> FOM:0.27 and only 54 residues ( that too wrongly) were built out of  
> 129.(CC=0.4), R=0.49 and Rfree=0.574.
> Regrading the data quality, Rsym:0.0448, Ranom:0.055, Resln:25.0-2.6A
> Spacegroup is P43212, completeness:99.4%, Multiplicity:11.7, anomalos
> signal is 1.52 at lowest resoln and higher in high resolution shells.
> What might be reason for not  able to solve this structure?
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Francis Reyes M.Sc.
215 UCB
University of Colorado at Boulder

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