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Rwork = 0.26 and Rfree = 0.32 are not necessarily unacceptably high for a 2.3 A dataset in my opinion. Not all crystals are the same, some just have more disorder than others and not all of this disorder is modelable (if that is a word). Having said that: - is the 2.3A data cutoff perhaps a tad optimistic and is your structure really more like 2.5-2.7A? - have you correctly modelled solvent/ions etc.? - did you try TLS analysis and refinement? - is yours a protein/DNA complex? I understand they often have a higher R-factors, the specialists may contribute their opinions on the reason (disorder in DNA? restraints for nucleic acids being less good than for protein?). From the information you give, I think you can be confident about the P21212 spacegroup. Mark Mark J. van Raaij Dpto de Bioquímica, Facultad de Farmacia Universidad de Santiago 15782 Santiago de Compostela Spain http://web.usc.es/~vanraaij/ researcherID: B-3678-2009 On 3 Dec 2009, at 18:49, Robert Radford wrote: > Hello- > > I am working up a data that is giving me unacceptable high R factors. > > > I am solving a data set that is good to ~ 2.3 Å using molecular > replacement based on a previously crystalized variant. The maps look > good with all the density fitting well to my model. I originally > worked up the data using PHASER for the molecular replacement. It > searched all alternative orthorhombic space groups and found a > single solution in P2(1)2(1)2 but that only gave me final R factors > of (Rwork = 0.26 and Rfree = 0.32) Next I went back and tried to > work the data up in a different space group. Thus far I have tried > P21 and P1. Both these space groups give me essential the same final > statistics (~Rwork = 0.26 and Rfree = 0.32). Furthermore, the > solution looks the same, the only change being the number for > monomers in the asymmetric unit (1, 2, 4 for P21212, P21 and P1 > respectively) The diagnostics don't indicate that the crystal is > twined and the data set looks good (i.e. the spots are nice and well > separated) > > The unit cell dimensions for the three cases as > > P1: a = 34.55 b = 46.95 c = 88.56, alpha = 89.94, beta = 90.03 > gamma = 89.99 > P21: a = 46.91 b = 34.52 c = 88.47, alpha = 90 , beta = 90.03 > gamma = 90.0 > P21212 a = 88.44 b = 34.51 c = 46.89, alpha = 90.0, beta = 90.00 > gamma = 90.0 > > One possible complication is that the biological unit is dimeric > with 2 fold symmetry. The 2 fold symmetry axis for the protein > appears to be sitting on a 2-fold crystallographic axis. > > Any suggestions? > > Thank you in advance. > Robert > ________________ > Robert Radford > > Graduate Researcher > Dept. Of Chemistry > UC San Diego