Hi again, I should have mentioned that, if you have a good enough model, it’s often possible to solve the structure in P1. The molecular replacement solution will settle on one of the twin domains (or you may end up with more than one solution, related by the twin law(s)). Then the symmetry of the solution will tell you the true symmetry of the crystal. Otherwise, you’ll have to test all the subgroups, and there will be a lot of those for P6322, especially if you’re not sure about screw axes.
But the true point group symmetry will only be lower than the symmetry in which the data merge if there’s twinning, which is why I’m wondering whether there are indications of twinning. It probably bears repeating that, if you test data merged in too low symmetry, the twinning tests that depend on twin laws can be misleading, because they look for reflections that are similar over a possible twin law. You need to have independent evidence from tests that do not depend on twin laws (i.e. statistical tests such as the moment tests or the L-test) that the data are perturbed in a way that implies twinning. Randy On 1 Oct 2014, at 03:02, Jurgen Bosch <[email protected]> wrote: > Dear BB, or in particular Phaser developers :-) > > This must be part of British humor right (or was that the Canadian influence > Randy) ? > > eLLG indicates that placement of ensemble "ensemble_1" will be straightforward > The data are sufficient to exceed the eLLG target > > The search space is finite 143 x 143 x 80 Å with 3 or 4 molecules per asu, > but Phaser has been burning CPU cycles quite a bit, we are approaching 24h by > now. Data extends to 1.7 Å - for MR we cut at 2.5 Å. > > I can hear Garib, yes, Molrep was done in few minutes but I’m not super > convinced about the solution either. Same with BALBES and MrBump (which took > a few more minutes, actually also days for MrBump) > > The space group appears to be P63 22 as judged by XDS, pointless, xtriage, > however the crystals are split (at least in some areas it’s visible) but I > thought XDS would take care of these “aliens” and eliminate them mostly. My > graduate student, Lauren, found a nifty program called DIALS that we wish to > explore further to rescue the “nice” data we have and hopefully solve the > structure. > > Lower symmetry space groups were tried down to P21 with increasing number of > molecules per asu and applying twin laws if necessary. The minor problem with > the twins is how do I really know that it is a higher symmetry space group > and not a 50% twin in a lower symmetry ? Rwork/Rfree in this particular case > do not seem to help at all for distinguishing between the solutions. Maps > looks sort of right but R-factors are not reflecting what you see on the > screen. > > We appreciate any suggestions and ideas what else we could do. > > Thanks, > > Jürgen > > ...................... > Jürgen Bosch > Johns Hopkins University > Bloomberg School of Public Health > Department of Biochemistry & Molecular Biology > Johns Hopkins Malaria Research Institute > 615 North Wolfe Street, W8708 > Baltimore, MD 21205 > Office: +1-410-614-4742 > Lab: +1-410-614-4894 > Fax: +1-410-955-2926 > http://lupo.jhsph.edu > ------ 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
