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Hi Yi, This Rfactor/Rfree behaviour is certainly something that is encountered in cases of partial twinning. What are the unit cell dimentions and space group of your crystal? See http://www.ccp4.ac.uk/html/twinning.html#frequently_enc for some space groups that support twinning. Note that if you run sfcheck with data indexed with a lower symmetry than that of the actual space group, it may report a partial twinning fraction close to 0.5, which would be an artefact of symmetry operators coinciding with twinning operators. Cheers, James On 31/05/06, Yi Xue <[EMAIL PROTECTED]> wrote:
*** 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
-- Dr. James Irving NH&MRC C.J. Martin Fellow Division of Structural Biology Wellcome Trust Centre for Human Genetics Oxford University Roosevelt Drive Headington, Oxford OX3 7BN UK email: [EMAIL PROTECTED] phone: +44 1865 287 550 (temporary)
