Hi, If you're unlucky, a combination of pseudo-symmetry and twinning gives only weak indications of twinning, because the twin-related reflections are correlated but the twinning tests assume that they are not. It might be worth considering that possibility. You could try solving the structure in lower symmetry space groups to see whether you get a solution that does not exactly obey the higher symmetry. Are you really certain about the space group? If one symmetry operator is wrong (e.g. a 2-fold instead of a 2-fold screw), some of the symmetry operators are still right, and you can get an apparent solution that partly explains the data. It might be worth running tests in all the variants of P422 as well. Best wishes Randy Read On 23 Jul 2009, at 22:54, [email protected] wrote:
Hi Francis, Thanks for your response. The matthews coefficient suggests two molecules in the AU. Phaser also finds two molecules. I ran the dataset through phenix xtriage it did not indicate twinning though. The molecule also exists in nature as a monomer. Shya
Twinning? What's your matthews coefficient say? Do you know if your structure is a multimer (biochemistry, etc)? Does it agree with the matthews coefficient?
If the unit cell is not big enough to hold all of the contents,then this is an indicator for twinning .
FR
On Jul 23, 2009, at 3:09 PM, [email protected] wrote:
Hi all,
I was trying to solve a structure by molecular replacement. I scaled the data in P4222 space group (resolution 2.7A) with two molecules in the assymmetric unit (molecule A and B) I ran phaser with my model and got a Zscore of 5.1. When I look at the map that I got from phaser I could easily see good electron density for both molecules, However upon inspection of the electron density map there were considerable interaction or clashes with molecule B and a symmetry atom. Molecule A had no clashes however with the symmetry atoms. I was wondering if anyone knows how to resolve this. Could it be a problem of space group. The statistics are good for space group P4222 and the I/sigI was good till 2.7A. Any advice is appreciated, Shya
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--------------------------------------------- Francis Reyes M.Sc. 215 UCB University of Colorado at Boulder
gpg --keyserver pgp.mit.edu --recv-keys 67BA8D5D
8AE2 F2F4 90F7 9640 28BC 686F 78FD 6669 67BA 8D5D
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------ Randy J. Read Department of Haematology, University of Cambridge Cambridge Institute for Medical Research Tel: + 44 1223 336500 Wellcome Trust/MRC Building Fax: + 44 1223 336827 Hills Road E-mail: [email protected] Cambridge CB2 0XY, U.K. www- structmed.cimr.cam.ac.uk