Hi, You don't say whether you've considered the possibility that the true symmetry is higher than P61, e.g. P6122. If there's higher symmetry consistent with your data, then either pointless or xtriage will tell you which space groups to consider for test refinements. Another good test (if you haven't allowed NCS-related copies to diverge in the refinement in P61) is the R vs R test, to tell whether the apparent twin operator is really a symmetry operator in the model.
Note that the R-factors aren't the best indicator, as they tend to drop when you assume perfect twinning, even if it doesn't exist. I think Garib has some of his talks on the web, giving some indication of what you can expect. Regards, Randy Read On 3 Mar 2010, at 04:35, subhash C bihani wrote: > Hi > > i am refining a protein strucutre with space group P61. Intesity statistics > doesnot suggest any twining but refmac and phenix xtriage suggest a twin > operator with fraction 0.48. when refined with this twin operator R factors > come dowm by 3-5% and also map looks much better. but upon closer inspceion it > seems that maps are heavily biased toward the model in both refmac and phenix > ( > I have mutated one lysine to his and it changed the map to cover his). my > question is why twin refinement maps are biased and what are the ways to > overcome this. > > my second question is how to decide whether to use twin refinement or not. is > it > depends on R factor statistics or we have to check some other parameters. > > thanks in advance > subhash bihani > scientific officer > Bhabha Atomic Research Centre > Trombay-400085 > Mumbai(M.S.) > India > Ph. +912594688 (o) > +919322191020 > subhash bihani > scientific officer > Bhabha Atomic Research Centre > Trombay-400085 > Mumbai(M.S.) > India > Ph. +912594688 (o) > +919322191020 > subhash bihani > scientific officer > Bhabha Atomic Research Centre > Trombay-400085 > Mumbai(M.S.) > India > Ph. +912594688 (o) > +919322191020 > > > > > > ------------------------------------------------- ------ 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: rj...@cam.ac.uk Cambridge CB2 0XY, U.K. www-structmed.cimr.cam.ac.uk
