Just to follow up on what has already been said: The twinning tests in truncate, phenix.xtriage and (since recently) in Phaser should give you a good idea whether the data might be twinned. If you have merged the data with too high symmetry, there won't be a potential twin operator (because it has been interpreted as a crystallographic symmetry operator) so you can't use things like the L test, but the moment tests are still useful.
If these tests do indicate twinning, then the true symmetry is probably lower, and there are many subgroups for P6222 that could be the true space group. You could investigate them systematically, but with a 42% identical model you might be able to sort it out by molecular replacement. In a number of cases we've succeeded in solving a structure using data merged in P1, and then using the symmetry of the resulting model to determine the space group. It's worth a try, especially if the MR attempts in P6222 gave a reasonable peak for the rotation search. Best wishes, Randy Read On 22 Jan 2013, at 06:25, LISA wrote: > Hi all, > Does anyone know how to check a data is twin and how to detwin? > My data is 3.3 A with space group P6222 or P6422? But I can not solve this > structue by molecular replacement with the model has 42% sequence identity. I > am wondering my data maybe twin. > Thanks > Lisa ------ 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
