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
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