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Dear all, There were some comments about detector issues, but these can be ruled out, to my opinion, since the lines appeared on different beamlines. Default settings of mosflm (spot picking) finds the cell 34 34 34 90 90 90 (pointless indicating P41212) Structure was solved by SAD phasing on the phosphates in this space group. Double helices stack in continuous helices, the backbone is well defined in the (refined) density maps but the individual bases are messy (purines and pyrimidines seemed to overlap) + obviously not all spots were covered and the duplex does not fit in the A.U. For this reason the integration was repeated in the higher cell 34 34 170 Space group most probably P212121, but solutions can be found in P41212 as well (still disordered bases) There are also indications that the 41 screw axis is rather a pseudo axis than a pure crystallographic one, also in the small cell Reindexing the cell to 34 34 340 also gives a solution, which supports the theory of Holton Rmerg is around 5% for the small cell, about 8% for the 170Å cell (both in P41212) Which refinement procedure would be best to follow? kind regards Margriet Margriet Ovaere Chemistry Department K.U.Leuven Biomolecular Architecture Celestijnenlaan 200 F B-3001 Heverlee (Leuven) Tel: +32(0)16327477 Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm