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Dear Veronica, I would not expect SHELX to work at all well at that resolution - I believe the resolution limit can be pushed out to about 2.5A in the presence of NCS. My suggestion would be to use CNS with torsional refinement, use strict constraints if possible (i.e refine a set of coordinates representative of one monomer and 4 rotation/translation matrices), and build into an averaged map (using the script in CNS or the option in COOT). It may help to average twin-related reflections to remove ambiguity in the estimation of the twinning factor, as suggested in Yeates Methods Enzymol 276:344-360. We have solved a twinned structure at this resolution, see the article and supplemental materials: McGowan et al EMBO J. 2006 25:3144-55. Good luck! James -- 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
