Hello,
I am carrying out molecular replacement on one of our recent data set using Phaser-MR. The data set was indexed P1 to 2.5 Angstorm. In my initial run, Phaser-MR returned the following:
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TWINNING
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tNCS/Twin Detection Table
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-Second Moments- --P-values--
Centric Acentric untwinned twin frac <5%
Theoretical for untwinned 3.00 2.00
Theoretical for perfect twin 2.00 1.50
Initial (data as input) 0.00 2.41+/-0.070 1 1
After Anisotropy Correction 0.00 2.12+/-0.052 1 1
After Anisotropy and tNCS ---n/a---
P-value < 0.01 for <5% twinned is considered significant
Resolution for Twin Analysis (85% I/SIGI > 3): 3.54A (HiRes= 2.67A)
Afterward the initial run I tried to re-run the job keeping all input mtz and model pdb and other parameters the same. (I simply click 'ReRun job' on the menu.) The only adjustments were (1) ensemble IDENT from 90% to 95%; (2) No. of copies to search for from 2 to 1. This time the programme warns of significant twinning:
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TWINNING
--------
tNCS/Twin Detection Table
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-Second Moments- --P-values--
Centric Acentric untwinned twin frac <5%
Theoretical for untwinned 3.00 2.00
Theoretical for perfect twin 2.00 1.50
Initial (data as input) 0.00 1.35+/-0.013 0 0
After Anisotropy Correction 0.00 1.29+/-0.011 0 0
After Anisotropy and tNCS ---n/a---
P-value < 0.01 for <5% twinned is considered significant
Resolution for Twin Analysis (85% I/SIGI > 3): 3.15A (HiRes= 2.67A)
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Warning: Intensity moments suggest significant twinning (>5%). Tests based on
possible twin laws will be more definitive.
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To my understanding Phaser first treats the data for twin / not twin before it really puts in the model. Thus I am curious why the same set of input data and model give different results in Twinning test?
Thanks!
Sam
PhD Candidate, The Chinese University of Hong Kong
