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To decide whether the resolution is good enough for small molecule direct methods, I prefer to use the traditional I > 2sigma(I) cutoff. Modern refinement programs can extract useful information at lower resolution than that. If you really have I >2sigma(I) to 1.14A then it would be worth trying shelxd for native direct methods. You will have to be patient, a recent comparable RNA structure took it a week to solve on an 8-CPU computer (Angew. Chem. Int. Ed. 52 (2013) 10370-10373), but then it found almost every atom. The advantage of direct methods is that they do not require a model, and since only about half of your molecule would fit into the asymmetric unit, it may not be exactly what you are hoping for. George On 05/22/2016 10:25 PM, Rafal Dolot wrote: > Dear CCP4 users, > > I think it is good place to ask for help. Last time I've tried > crystallize a one interesting DNA oligo molecule with 52 bases. I've > expected self-association of the molecule with hairpin duplex > structure and a loop in the middle of this construct. After three > years of fails and salts crystals, I recorded data up to 1.14 A, > Rmerge 8.4%, SG C2, unit cell 49.42 24.69 50.23 90.00 118.48 90.00. > Judging from Matthews coeff. it looks like the content is smaller than > expected. I've tried use several models for MR - single and duplex > structures of DNA with different length, as well as some fragments of > single stranded structures e.g. aptamers of dnazymes. And still no > solution. Is it possible to solve this structure by another method > using only this native dataset? > > Best regards > > Rafal > -- Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-33021 or -33068 Fax. +49-551-39-22582