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Hey Yi! I had almost the same problems with a twinned crystal... the solution was refinement with SHELXL using the TWIN and BASF commands. the only thing you have to find out is the symmetry relationship between the twin domains (twin law). Look for another indexing possibility for your crystal, the symmetry relationship between this space group and your original one would be the twin law. There is also a lookup table for possible twin laws of merohedrally twinned crystals on the ccp4 homepage (http://www.ccp4.ac.uk/html/twinning.html). The BASF command defines the twin fraction, the relative proportion of the twin domains, an estimate is given by SFCHECK, but it will be refined by SHELXL. Using this refinement procedure decreased R/Rfree >15% in my case! good luck, david > -------- Original-Nachricht -------- > Datum: Wed, 31 May 2006 17:36:21 -0500 > Von: Yi Xue <[EMAIL PROTECTED]> > An: <[email protected]> > Betreff: [ccp4bb]: Rfree can not be decreased > > *** For details on how to be removed from this list visit the *** > *** CCP4 home page http://www.ccp4.ac.uk *** > > Hi, all: > I tried to solve a protein structure by molecular replacement. The apo > form is already solved, I crystallized it with Cu(II). The data diffracted > to 1.6A, the highest resolution shell has more than 80% completeness, R is > 43%. > I used phaser to find the MR solutin ,then used Refmac to do rigid body > refinement, and restrained refinement. I adjusted weighing factor to keep > chi^2 exactly 0.01. After these steps, R is around 0.30, Rfree is about > 0.37. > Then I fed all the data to arp/warp, it showed that while R decresed, > Rfree increased, and finally, Rfree is around 40%. > I tried to manual build the model, however, I found that most density > were unambigously assigned. I only need to do some small adjustments, > these > minor adjustments did not improve R factors a lot. > All suggestions are highly appreciated. > > Best regards > Yi > -- Der GMX SmartSurfer hilft bis zu 70% Ihrer Onlinekosten zu sparen! Ideal für Modem und ISDN: http://www.gmx.net/de/go/smartsurfer
